[syzbot] [mm?] kernel BUG in move_pages

[syzbot] [mm?] kernel BUG in move_pages

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz

The issue was bisected to:

commit adef440691bab824e39c1b17382322d195e1fab0
Author: Andrea Arcangeli <aarcange@redhat.com>
Date:   Wed Dec 6 10:36:56 2023 +0000

    userfaultfd: UFFDIO_MOVE uABI

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")

 do_one_initcall+0x128/0x680 init/main.c:1237
 do_initcall_level init/main.c:1299 [inline]
 do_initcalls init/main.c:1315 [inline]
 do_basic_setup init/main.c:1334 [inline]
 kernel_init_freeable+0x692/0xc30 init/main.c:1552
 kernel_init+0x1c/0x2a0 init/main.c:1442
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
------------[ cut here ]------------
kernel BUG at include/linux/page-flags.h:1035!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 userfaultfd_move fs/userfaultfd.c:2047 [inline]
 userfaultfd_ioctl+0x683/0x6420 fs/userfaultfd.c:2169
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl fs/ioctl.c:857 [inline]
 __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xd0/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x62/0x6a
RIP: 0033:0x7f4bada9b3e9
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff2c1d6998 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fff2c1d6b68 RCX: 00007f4bada9b3e9
RDX: 00000000200000c0 RSI: 00000000c028aa05 RDI: 0000000000000003
RBP: 00007f4badb0e610 R08: 00007fff2c1d6b68 R09: 00007fff2c1d6b68
R10: 00007fff2c1d6b68 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fff2c1d6b58 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan]

On Thu, Jan 11, 2024 at 8:25 AM syzbot
<syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
>
> The issue was bisected to:
>
> commit adef440691bab824e39c1b17382322d195e1fab0
> Author: Andrea Arcangeli <aarcange@redhat.com>
> Date:   Wed Dec 6 10:36:56 2023 +0000
>
>     userfaultfd: UFFDIO_MOVE uABI
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
>
>  do_one_initcall+0x128/0x680 init/main.c:1237
>  do_initcall_level init/main.c:1299 [inline]
>  do_initcalls init/main.c:1315 [inline]
>  do_basic_setup init/main.c:1334 [inline]
>  kernel_init_freeable+0x692/0xc30 init/main.c:1552
>  kernel_init+0x1c/0x2a0 init/main.c:1442
>  ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> ------------[ cut here ]------------
> kernel BUG at include/linux/page-flags.h:1035!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]

From a quick look, I think the new ioctl is being used against a
file-backed page and that's why PageAnonExclusive() throws this error.
I'll confirm if this is indeed the case and will add checks for that
case. Thanks!

> RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
> Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
> RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
> RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
> RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
> R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
> FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  userfaultfd_move fs/userfaultfd.c:2047 [inline]
>  userfaultfd_ioctl+0x683/0x6420 fs/userfaultfd.c:2169
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl fs/ioctl.c:857 [inline]
>  __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xd0/0x250 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x62/0x6a
> RIP: 0033:0x7f4bada9b3e9
> Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fff2c1d6998 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007fff2c1d6b68 RCX: 00007f4bada9b3e9
> RDX: 00000000200000c0 RSI: 00000000c028aa05 RDI: 0000000000000003
> RBP: 00007f4badb0e610 R08: 00007fff2c1d6b68 R09: 00007fff2c1d6b68
> R10: 00007fff2c1d6b68 R11: 0000000000000246 R12: 0000000000000001
> R13: 00007fff2c1d6b58 R14: 0000000000000001 R15: 0000000000000001
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
> Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
> RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
> RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
> RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
> R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
> FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan]

On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Thu, Jan 11, 2024 at 8:25 AM syzbot
> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> > git tree:       linux-next
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> > dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
> >
> > The issue was bisected to:
> >
> > commit adef440691bab824e39c1b17382322d195e1fab0
> > Author: Andrea Arcangeli <aarcange@redhat.com>
> > Date:   Wed Dec 6 10:36:56 2023 +0000
> >
> >     userfaultfd: UFFDIO_MOVE uABI
> >
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> >
> >  do_one_initcall+0x128/0x680 init/main.c:1237
> >  do_initcall_level init/main.c:1299 [inline]
> >  do_initcalls init/main.c:1315 [inline]
> >  do_basic_setup init/main.c:1334 [inline]
> >  kernel_init_freeable+0x692/0xc30 init/main.c:1552
> >  kernel_init+0x1c/0x2a0 init/main.c:1442
> >  ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> >  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> > ------------[ cut here ]------------
> > kernel BUG at include/linux/page-flags.h:1035!
> > invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> > CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> > RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
>
> From a quick look, I think the new ioctl is being used against a
> file-backed page and that's why PageAnonExclusive() throws this error.
> I'll confirm if this is indeed the case and will add checks for that
> case. Thanks!

Hmm. Looking at the reproducer it does not look like a file-backed
memory... Anyways, I'm on it.

>
> > RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
> > Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
> > RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
> > RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
> > RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
> > RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
> > R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
> > R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
> > FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  <TASK>
> >  userfaultfd_move fs/userfaultfd.c:2047 [inline]
> >  userfaultfd_ioctl+0x683/0x6420 fs/userfaultfd.c:2169
> >  vfs_ioctl fs/ioctl.c:51 [inline]
> >  __do_sys_ioctl fs/ioctl.c:871 [inline]
> >  __se_sys_ioctl fs/ioctl.c:857 [inline]
> >  __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xd0/0x250 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x62/0x6a
> > RIP: 0033:0x7f4bada9b3e9
> > Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007fff2c1d6998 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 00007fff2c1d6b68 RCX: 00007f4bada9b3e9
> > RDX: 00000000200000c0 RSI: 00000000c028aa05 RDI: 0000000000000003
> > RBP: 00007f4badb0e610 R08: 00007fff2c1d6b68 R09: 00007fff2c1d6b68
> > R10: 00007fff2c1d6b68 R11: 0000000000000246 R12: 0000000000000001
> > R13: 00007fff2c1d6b58 R14: 0000000000000001 R15: 0000000000000001
> >  </TASK>
> > Modules linked in:
> > ---[ end trace 0000000000000000 ]---
> > RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> > RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
> > Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
> > RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
> > RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
> > RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
> > RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
> > R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
> > R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
> > FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@googlegroups.com.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> >
> > If the report is already addressed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> >
> > If you want syzbot to run the reproducer, reply with:
> > #syz test: git://repo/address.git branch-or-commit-hash
> > If you attach or paste a git patch, syzbot will apply it before testing.
> >
> > If you want to overwrite report's subsystems, reply with:
> > #syz set subsystems: new-subsystem
> > (See the list of subsystem names on the web dashboard)
> >
> > If the report is a duplicate of another one, reply with:
> > #syz dup: exact-subject-of-another-report
> >
> > If you want to undo deduplication, reply with:
> > #syz undup

Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan]

On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > On Thu, Jan 11, 2024 at 8:25 AM syzbot
> > <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
> > >
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> > > git tree:       linux-next
> > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> > > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
> > >
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
> > >
> > > The issue was bisected to:
> > >
> > > commit adef440691bab824e39c1b17382322d195e1fab0
> > > Author: Andrea Arcangeli <aarcange@redhat.com>
> > > Date:   Wed Dec 6 10:36:56 2023 +0000
> > >
> > >     userfaultfd: UFFDIO_MOVE uABI
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> > > final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> > > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> > >
> > >  do_one_initcall+0x128/0x680 init/main.c:1237
> > >  do_initcall_level init/main.c:1299 [inline]
> > >  do_initcalls init/main.c:1315 [inline]
> > >  do_basic_setup init/main.c:1334 [inline]
> > >  kernel_init_freeable+0x692/0xc30 init/main.c:1552
> > >  kernel_init+0x1c/0x2a0 init/main.c:1442
> > >  ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> > >  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> > > ------------[ cut here ]------------
> > > kernel BUG at include/linux/page-flags.h:1035!
> > > invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> > > CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> > > RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> >
> > From a quick look, I think the new ioctl is being used against a
> > file-backed page and that's why PageAnonExclusive() throws this error.
> > I'll confirm if this is indeed the case and will add checks for that
> > case. Thanks!
>
> Hmm. Looking at the reproducer it does not look like a file-backed
> memory... Anyways, I'm on it.

Looks like the test is trying to move the huge_zero_page. Wonder how
we should handle this. Just fail or do something else? Adding David
and Peter for feedback.

>
> >
> > > RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
> > > Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
> > > RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
> > > RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
> > > RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
> > > RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
> > > R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
> > > R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
> > > FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > Call Trace:
> > >  <TASK>
> > >  userfaultfd_move fs/userfaultfd.c:2047 [inline]
> > >  userfaultfd_ioctl+0x683/0x6420 fs/userfaultfd.c:2169
> > >  vfs_ioctl fs/ioctl.c:51 [inline]
> > >  __do_sys_ioctl fs/ioctl.c:871 [inline]
> > >  __se_sys_ioctl fs/ioctl.c:857 [inline]
> > >  __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
> > >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > >  do_syscall_64+0xd0/0x250 arch/x86/entry/common.c:83
> > >  entry_SYSCALL_64_after_hwframe+0x62/0x6a
> > > RIP: 0033:0x7f4bada9b3e9
> > > Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > > RSP: 002b:00007fff2c1d6998 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > > RAX: ffffffffffffffda RBX: 00007fff2c1d6b68 RCX: 00007f4bada9b3e9
> > > RDX: 00000000200000c0 RSI: 00000000c028aa05 RDI: 0000000000000003
> > > RBP: 00007f4badb0e610 R08: 00007fff2c1d6b68 R09: 00007fff2c1d6b68
> > > R10: 00007fff2c1d6b68 R11: 0000000000000246 R12: 0000000000000001
> > > R13: 00007fff2c1d6b58 R14: 0000000000000001 R15: 0000000000000001
> > >  </TASK>
> > > Modules linked in:
> > > ---[ end trace 0000000000000000 ]---
> > > RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> > > RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
> > > Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
> > > RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
> > > RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
> > > RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
> > > RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
> > > R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
> > > R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
> > > FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > >
> > >
> > > ---
> > > This report is generated by a bot. It may contain errors.
> > > See https://goo.gl/tpsmEJ for more information about syzbot.
> > > syzbot engineers can be reached at syzkaller@googlegroups.com.
> > >
> > > syzbot will keep track of this issue. See:
> > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> > >
> > > If the report is already addressed, let syzbot know by replying with:
> > > #syz fix: exact-commit-title
> > >
> > > If you want syzbot to run the reproducer, reply with:
> > > #syz test: git://repo/address.git branch-or-commit-hash
> > > If you attach or paste a git patch, syzbot will apply it before testing.
> > >
> > > If you want to overwrite report's subsystems, reply with:
> > > #syz set subsystems: new-subsystem
> > > (See the list of subsystem names on the web dashboard)
> > >
> > > If the report is a duplicate of another one, reply with:
> > > #syz dup: exact-subject-of-another-report
> > >
> > > If you want to undo deduplication, reply with:
> > > #syz undup

Re: [syzbot] [mm?] kernel BUG in move_pages

[David Hildenbrand]

On 11.01.24 19:34, Suren Baghdasaryan wrote:
> On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@google.com> wrote:
>>
>> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
>>>
>>> On Thu, Jan 11, 2024 at 8:25 AM syzbot
>>> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
>>>>
>>>> Hello,
>>>>
>>>> syzbot found the following issue on:
>>>>
>>>> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
>>>> git tree:       linux-next
>>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
>>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
>>>>
>>>> Downloadable assets:
>>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
>>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
>>>>
>>>> The issue was bisected to:
>>>>
>>>> commit adef440691bab824e39c1b17382322d195e1fab0
>>>> Author: Andrea Arcangeli <aarcange@redhat.com>
>>>> Date:   Wed Dec 6 10:36:56 2023 +0000
>>>>
>>>>      userfaultfd: UFFDIO_MOVE uABI
>>>>
>>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
>>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
>>>>
>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
>>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
>>>>
>>>>   do_one_initcall+0x128/0x680 init/main.c:1237
>>>>   do_initcall_level init/main.c:1299 [inline]
>>>>   do_initcalls init/main.c:1315 [inline]
>>>>   do_basic_setup init/main.c:1334 [inline]
>>>>   kernel_init_freeable+0x692/0xc30 init/main.c:1552
>>>>   kernel_init+0x1c/0x2a0 init/main.c:1442
>>>>   ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
>>>>   ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
>>>> ------------[ cut here ]------------
>>>> kernel BUG at include/linux/page-flags.h:1035!
>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>>>> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
>>>> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
>>>
>>>  From a quick look, I think the new ioctl is being used against a
>>> file-backed page and that's why PageAnonExclusive() throws this error.
>>> I'll confirm if this is indeed the case and will add checks for that
>>> case. Thanks!
>>
>> Hmm. Looking at the reproducer it does not look like a file-backed
>> memory... Anyways, I'm on it.
> 
> Looks like the test is trying to move the huge_zero_page. Wonder how
> we should handle this. Just fail or do something else? Adding David
> and Peter for feedback.

You'll need some special-casing to handle that. But it should be fairly 
easy.

-- 
Cheers,

David / dhildenb

Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan]

On Thu, Jan 11, 2024 at 6:58 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 11.01.24 19:34, Suren Baghdasaryan wrote:
> > On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >>
> >> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >>>
> >>> On Thu, Jan 11, 2024 at 8:25 AM syzbot
> >>> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
> >>>>
> >>>> Hello,
> >>>>
> >>>> syzbot found the following issue on:
> >>>>
> >>>> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> >>>> git tree:       linux-next
> >>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> >>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> >>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> >>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> >>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
> >>>>
> >>>> Downloadable assets:
> >>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> >>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> >>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
> >>>>
> >>>> The issue was bisected to:
> >>>>
> >>>> commit adef440691bab824e39c1b17382322d195e1fab0
> >>>> Author: Andrea Arcangeli <aarcange@redhat.com>
> >>>> Date:   Wed Dec 6 10:36:56 2023 +0000
> >>>>
> >>>>      userfaultfd: UFFDIO_MOVE uABI
> >>>>
> >>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> >>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
> >>>>
> >>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >>>> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> >>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> >>>>
> >>>>   do_one_initcall+0x128/0x680 init/main.c:1237
> >>>>   do_initcall_level init/main.c:1299 [inline]
> >>>>   do_initcalls init/main.c:1315 [inline]
> >>>>   do_basic_setup init/main.c:1334 [inline]
> >>>>   kernel_init_freeable+0x692/0xc30 init/main.c:1552
> >>>>   kernel_init+0x1c/0x2a0 init/main.c:1442
> >>>>   ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> >>>>   ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> >>>> ------------[ cut here ]------------
> >>>> kernel BUG at include/linux/page-flags.h:1035!
> >>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> >>>> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> >>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> >>>> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> >>>
> >>>  From a quick look, I think the new ioctl is being used against a
> >>> file-backed page and that's why PageAnonExclusive() throws this error.
> >>> I'll confirm if this is indeed the case and will add checks for that
> >>> case. Thanks!
> >>
> >> Hmm. Looking at the reproducer it does not look like a file-backed
> >> memory... Anyways, I'm on it.
> >
> > Looks like the test is trying to move the huge_zero_page. Wonder how
> > we should handle this. Just fail or do something else? Adding David
> > and Peter for feedback.
>
> You'll need some special-casing to handle that. But it should be fairly
> easy.

Ok, so should we treat zeropage the same as PAE and map destination
PTE/PMD to zeropage while clearing source PTE/PMD?

>
> --
> Cheers,
>
> David / dhildenb
>

Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan]

On Thu, Jan 11, 2024 at 9:00 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 11.01.24 21:20, Suren Baghdasaryan wrote:
> > On Thu, Jan 11, 2024 at 6:58 PM David Hildenbrand <david@redhat.com> wrote:
> >>
> >> On 11.01.24 19:34, Suren Baghdasaryan wrote:
> >>> On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >>>>
> >>>> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >>>>>
> >>>>> On Thu, Jan 11, 2024 at 8:25 AM syzbot
> >>>>> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
> >>>>>>
> >>>>>> Hello,
> >>>>>>
> >>>>>> syzbot found the following issue on:
> >>>>>>
> >>>>>> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> >>>>>> git tree:       linux-next
> >>>>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> >>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> >>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> >>>>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> >>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> >>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
> >>>>>>
> >>>>>> Downloadable assets:
> >>>>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> >>>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> >>>>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
> >>>>>>
> >>>>>> The issue was bisected to:
> >>>>>>
> >>>>>> commit adef440691bab824e39c1b17382322d195e1fab0
> >>>>>> Author: Andrea Arcangeli <aarcange@redhat.com>
> >>>>>> Date:   Wed Dec 6 10:36:56 2023 +0000
> >>>>>>
> >>>>>>       userfaultfd: UFFDIO_MOVE uABI
> >>>>>>
> >>>>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> >>>>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> >>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
> >>>>>>
> >>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >>>>>> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> >>>>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> >>>>>>
> >>>>>>    do_one_initcall+0x128/0x680 init/main.c:1237
> >>>>>>    do_initcall_level init/main.c:1299 [inline]
> >>>>>>    do_initcalls init/main.c:1315 [inline]
> >>>>>>    do_basic_setup init/main.c:1334 [inline]
> >>>>>>    kernel_init_freeable+0x692/0xc30 init/main.c:1552
> >>>>>>    kernel_init+0x1c/0x2a0 init/main.c:1442
> >>>>>>    ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> >>>>>>    ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> >>>>>> ------------[ cut here ]------------
> >>>>>> kernel BUG at include/linux/page-flags.h:1035!
> >>>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> >>>>>> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> >>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> >>>>>> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> >>>>>
> >>>>>   From a quick look, I think the new ioctl is being used against a
> >>>>> file-backed page and that's why PageAnonExclusive() throws this error.
> >>>>> I'll confirm if this is indeed the case and will add checks for that
> >>>>> case. Thanks!
> >>>>
> >>>> Hmm. Looking at the reproducer it does not look like a file-backed
> >>>> memory... Anyways, I'm on it.
> >>>
> >>> Looks like the test is trying to move the huge_zero_page. Wonder how
> >>> we should handle this. Just fail or do something else? Adding David
> >>> and Peter for feedback.
> >>
> >> You'll need some special-casing to handle that. But it should be fairly
> >> easy.
> >
> > Ok, so should we treat zeropage the same as PAE and map destination
> > PTE/PMD to zeropage while clearing source PTE/PMD?
>
> Likely yes. So it's transparent for user space what we are moving. (this
> sounds like an easy case to not require a prior write access just to
> move it)

Ok, working on it. split_huge_pmd() already knows how to split
huge_zero_page but I think I'll need special handling in both
move_pages_pte() and move_pages_huge_pmd().

>
> --
> Cheers,
>
> David / dhildenb
>

Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan]

On Thu, Jan 11, 2024 at 1:06 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 11.01.24 22:04, Suren Baghdasaryan wrote:
> > On Thu, Jan 11, 2024 at 9:00 PM David Hildenbrand <david@redhat.com> wrote:
> >>
> >> On 11.01.24 21:20, Suren Baghdasaryan wrote:
> >>> On Thu, Jan 11, 2024 at 6:58 PM David Hildenbrand <david@redhat.com> wrote:
> >>>>
> >>>> On 11.01.24 19:34, Suren Baghdasaryan wrote:
> >>>>> On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >>>>>>
> >>>>>> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >>>>>>>
> >>>>>>> On Thu, Jan 11, 2024 at 8:25 AM syzbot
> >>>>>>> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
> >>>>>>>>
> >>>>>>>> Hello,
> >>>>>>>>
> >>>>>>>> syzbot found the following issue on:
> >>>>>>>>
> >>>>>>>> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> >>>>>>>> git tree:       linux-next
> >>>>>>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> >>>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> >>>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> >>>>>>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> >>>>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> >>>>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
> >>>>>>>>
> >>>>>>>> Downloadable assets:
> >>>>>>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> >>>>>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> >>>>>>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
> >>>>>>>>
> >>>>>>>> The issue was bisected to:
> >>>>>>>>
> >>>>>>>> commit adef440691bab824e39c1b17382322d195e1fab0
> >>>>>>>> Author: Andrea Arcangeli <aarcange@redhat.com>
> >>>>>>>> Date:   Wed Dec 6 10:36:56 2023 +0000
> >>>>>>>>
> >>>>>>>>        userfaultfd: UFFDIO_MOVE uABI
> >>>>>>>>
> >>>>>>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> >>>>>>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> >>>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
> >>>>>>>>
> >>>>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >>>>>>>> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> >>>>>>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> >>>>>>>>
> >>>>>>>>     do_one_initcall+0x128/0x680 init/main.c:1237
> >>>>>>>>     do_initcall_level init/main.c:1299 [inline]
> >>>>>>>>     do_initcalls init/main.c:1315 [inline]
> >>>>>>>>     do_basic_setup init/main.c:1334 [inline]
> >>>>>>>>     kernel_init_freeable+0x692/0xc30 init/main.c:1552
> >>>>>>>>     kernel_init+0x1c/0x2a0 init/main.c:1442
> >>>>>>>>     ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> >>>>>>>>     ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> >>>>>>>> ------------[ cut here ]------------
> >>>>>>>> kernel BUG at include/linux/page-flags.h:1035!
> >>>>>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> >>>>>>>> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> >>>>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> >>>>>>>> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> >>>>>>>
> >>>>>>>    From a quick look, I think the new ioctl is being used against a
> >>>>>>> file-backed page and that's why PageAnonExclusive() throws this error.
> >>>>>>> I'll confirm if this is indeed the case and will add checks for that
> >>>>>>> case. Thanks!
> >>>>>>
> >>>>>> Hmm. Looking at the reproducer it does not look like a file-backed
> >>>>>> memory... Anyways, I'm on it.
> >>>>>
> >>>>> Looks like the test is trying to move the huge_zero_page. Wonder how
> >>>>> we should handle this. Just fail or do something else? Adding David
> >>>>> and Peter for feedback.
> >>>>
> >>>> You'll need some special-casing to handle that. But it should be fairly
> >>>> easy.
> >>>
> >>> Ok, so should we treat zeropage the same as PAE and map destination
> >>> PTE/PMD to zeropage while clearing source PTE/PMD?
> >>
> >> Likely yes. So it's transparent for user space what we are moving. (this
> >> sounds like an easy case to not require a prior write access just to
> >> move it)
> >
> > Ok, working on it. split_huge_pmd() already knows how to split
> > huge_zero_page but I think I'll need special handling in both
> > move_pages_pte() and move_pages_huge_pmd().
>
> A PTE-mapped huge zeropage is just a page table populated with the
> ordinary shared zeropage. Are you moving the ordinary shared zeropage as
> well? If not, you should do so for consistency (or not do either :) ).

Yes, I think I should move ordinary zeropages as well.

>
> --
> Cheers,
>
> David / dhildenb
>

Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan]

On Thu, Jan 11, 2024 at 9:13 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Thu, Jan 11, 2024 at 1:06 PM David Hildenbrand <david@redhat.com> wrote:
> >
> > On 11.01.24 22:04, Suren Baghdasaryan wrote:
> > > On Thu, Jan 11, 2024 at 9:00 PM David Hildenbrand <david@redhat.com> wrote:
> > >>
> > >> On 11.01.24 21:20, Suren Baghdasaryan wrote:
> > >>> On Thu, Jan 11, 2024 at 6:58 PM David Hildenbrand <david@redhat.com> wrote:
> > >>>>
> > >>>> On 11.01.24 19:34, Suren Baghdasaryan wrote:
> > >>>>> On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > >>>>>>
> > >>>>>> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > >>>>>>>
> > >>>>>>> On Thu, Jan 11, 2024 at 8:25 AM syzbot
> > >>>>>>> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
> > >>>>>>>>
> > >>>>>>>> Hello,
> > >>>>>>>>
> > >>>>>>>> syzbot found the following issue on:
> > >>>>>>>>
> > >>>>>>>> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> > >>>>>>>> git tree:       linux-next
> > >>>>>>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> > >>>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> > >>>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> > >>>>>>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > >>>>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> > >>>>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
> > >>>>>>>>
> > >>>>>>>> Downloadable assets:
> > >>>>>>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> > >>>>>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> > >>>>>>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
> > >>>>>>>>
> > >>>>>>>> The issue was bisected to:
> > >>>>>>>>
> > >>>>>>>> commit adef440691bab824e39c1b17382322d195e1fab0
> > >>>>>>>> Author: Andrea Arcangeli <aarcange@redhat.com>
> > >>>>>>>> Date:   Wed Dec 6 10:36:56 2023 +0000
> > >>>>>>>>
> > >>>>>>>>        userfaultfd: UFFDIO_MOVE uABI
> > >>>>>>>>
> > >>>>>>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> > >>>>>>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> > >>>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
> > >>>>>>>>
> > >>>>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > >>>>>>>> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> > >>>>>>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> > >>>>>>>>
> > >>>>>>>>     do_one_initcall+0x128/0x680 init/main.c:1237
> > >>>>>>>>     do_initcall_level init/main.c:1299 [inline]
> > >>>>>>>>     do_initcalls init/main.c:1315 [inline]
> > >>>>>>>>     do_basic_setup init/main.c:1334 [inline]
> > >>>>>>>>     kernel_init_freeable+0x692/0xc30 init/main.c:1552
> > >>>>>>>>     kernel_init+0x1c/0x2a0 init/main.c:1442
> > >>>>>>>>     ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> > >>>>>>>>     ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> > >>>>>>>> ------------[ cut here ]------------
> > >>>>>>>> kernel BUG at include/linux/page-flags.h:1035!
> > >>>>>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> > >>>>>>>> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> > >>>>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> > >>>>>>>> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> > >>>>>>>
> > >>>>>>>    From a quick look, I think the new ioctl is being used against a
> > >>>>>>> file-backed page and that's why PageAnonExclusive() throws this error.
> > >>>>>>> I'll confirm if this is indeed the case and will add checks for that
> > >>>>>>> case. Thanks!
> > >>>>>>
> > >>>>>> Hmm. Looking at the reproducer it does not look like a file-backed
> > >>>>>> memory... Anyways, I'm on it.
> > >>>>>
> > >>>>> Looks like the test is trying to move the huge_zero_page. Wonder how
> > >>>>> we should handle this. Just fail or do something else? Adding David
> > >>>>> and Peter for feedback.
> > >>>>
> > >>>> You'll need some special-casing to handle that. But it should be fairly
> > >>>> easy.
> > >>>
> > >>> Ok, so should we treat zeropage the same as PAE and map destination
> > >>> PTE/PMD to zeropage while clearing source PTE/PMD?
> > >>
> > >> Likely yes. So it's transparent for user space what we are moving. (this
> > >> sounds like an easy case to not require a prior write access just to
> > >> move it)
> > >
> > > Ok, working on it. split_huge_pmd() already knows how to split
> > > huge_zero_page but I think I'll need special handling in both
> > > move_pages_pte() and move_pages_huge_pmd().
> >
> > A PTE-mapped huge zeropage is just a page table populated with the
> > ordinary shared zeropage. Are you moving the ordinary shared zeropage as
> > well? If not, you should do so for consistency (or not do either :) ).
>
> Yes, I think I should move ordinary zeropages as well.

I have a version that seems to work but I want to test it more and
it's too heavy to be considered a quick fix for linux-next. I'll post
a simple one-line fix which takes care of this crash and keeps the
behavior for zeropages the same (ioctl returns -EBUSY). Later will
post a separate patch to move huge and ordinary zeropages.

>
> >
> > --
> > Cheers,
> >
> > David / dhildenb
> >

Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan]

On Thu, Jan 11, 2024 at 3:23 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Thu, Jan 11, 2024 at 9:13 PM Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > On Thu, Jan 11, 2024 at 1:06 PM David Hildenbrand <david@redhat.com> wrote:
> > >
> > > On 11.01.24 22:04, Suren Baghdasaryan wrote:
> > > > On Thu, Jan 11, 2024 at 9:00 PM David Hildenbrand <david@redhat.com> wrote:
> > > >>
> > > >> On 11.01.24 21:20, Suren Baghdasaryan wrote:
> > > >>> On Thu, Jan 11, 2024 at 6:58 PM David Hildenbrand <david@redhat.com> wrote:
> > > >>>>
> > > >>>> On 11.01.24 19:34, Suren Baghdasaryan wrote:
> > > >>>>> On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > > >>>>>>
> > > >>>>>> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > > >>>>>>>
> > > >>>>>>> On Thu, Jan 11, 2024 at 8:25 AM syzbot
> > > >>>>>>> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
> > > >>>>>>>>
> > > >>>>>>>> Hello,
> > > >>>>>>>>
> > > >>>>>>>> syzbot found the following issue on:
> > > >>>>>>>>
> > > >>>>>>>> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> > > >>>>>>>> git tree:       linux-next
> > > >>>>>>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> > > >>>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> > > >>>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> > > >>>>>>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > > >>>>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> > > >>>>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
> > > >>>>>>>>
> > > >>>>>>>> Downloadable assets:
> > > >>>>>>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> > > >>>>>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> > > >>>>>>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
> > > >>>>>>>>
> > > >>>>>>>> The issue was bisected to:
> > > >>>>>>>>
> > > >>>>>>>> commit adef440691bab824e39c1b17382322d195e1fab0
> > > >>>>>>>> Author: Andrea Arcangeli <aarcange@redhat.com>
> > > >>>>>>>> Date:   Wed Dec 6 10:36:56 2023 +0000
> > > >>>>>>>>
> > > >>>>>>>>        userfaultfd: UFFDIO_MOVE uABI
> > > >>>>>>>>
> > > >>>>>>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> > > >>>>>>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> > > >>>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
> > > >>>>>>>>
> > > >>>>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > >>>>>>>> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> > > >>>>>>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> > > >>>>>>>>
> > > >>>>>>>>     do_one_initcall+0x128/0x680 init/main.c:1237
> > > >>>>>>>>     do_initcall_level init/main.c:1299 [inline]
> > > >>>>>>>>     do_initcalls init/main.c:1315 [inline]
> > > >>>>>>>>     do_basic_setup init/main.c:1334 [inline]
> > > >>>>>>>>     kernel_init_freeable+0x692/0xc30 init/main.c:1552
> > > >>>>>>>>     kernel_init+0x1c/0x2a0 init/main.c:1442
> > > >>>>>>>>     ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> > > >>>>>>>>     ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> > > >>>>>>>> ------------[ cut here ]------------
> > > >>>>>>>> kernel BUG at include/linux/page-flags.h:1035!
> > > >>>>>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> > > >>>>>>>> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> > > >>>>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> > > >>>>>>>> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> > > >>>>>>>
> > > >>>>>>>    From a quick look, I think the new ioctl is being used against a
> > > >>>>>>> file-backed page and that's why PageAnonExclusive() throws this error.
> > > >>>>>>> I'll confirm if this is indeed the case and will add checks for that
> > > >>>>>>> case. Thanks!
> > > >>>>>>
> > > >>>>>> Hmm. Looking at the reproducer it does not look like a file-backed
> > > >>>>>> memory... Anyways, I'm on it.
> > > >>>>>
> > > >>>>> Looks like the test is trying to move the huge_zero_page. Wonder how
> > > >>>>> we should handle this. Just fail or do something else? Adding David
> > > >>>>> and Peter for feedback.
> > > >>>>
> > > >>>> You'll need some special-casing to handle that. But it should be fairly
> > > >>>> easy.
> > > >>>
> > > >>> Ok, so should we treat zeropage the same as PAE and map destination
> > > >>> PTE/PMD to zeropage while clearing source PTE/PMD?
> > > >>
> > > >> Likely yes. So it's transparent for user space what we are moving. (this
> > > >> sounds like an easy case to not require a prior write access just to
> > > >> move it)
> > > >
> > > > Ok, working on it. split_huge_pmd() already knows how to split
> > > > huge_zero_page but I think I'll need special handling in both
> > > > move_pages_pte() and move_pages_huge_pmd().
> > >
> > > A PTE-mapped huge zeropage is just a page table populated with the
> > > ordinary shared zeropage. Are you moving the ordinary shared zeropage as
> > > well? If not, you should do so for consistency (or not do either :) ).
> >
> > Yes, I think I should move ordinary zeropages as well.
>
> I have a version that seems to work but I want to test it more and
> it's too heavy to be considered a quick fix for linux-next. I'll post
> a simple one-line fix which takes care of this crash and keeps the
> behavior for zeropages the same (ioctl returns -EBUSY). Later will
> post a separate patch to move huge and ordinary zeropages.

I posted a quick fix for this issue here:
https://lore.kernel.org/all/20240112013935.1474648-1-surenb@google.com/
It cleanly applies over linux-next, mm-stable and mm-unstable. Andrew,
Stephen, could you please pull the fix into your branches?
Thanks,
Suren.


>
> >
> > >
> > > --
> > > Cheers,
> > >
> > > David / dhildenb
> > >

Re: [syzbot] [mm?] kernel BUG in move_pages

[Stephen Rothwell]

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Hi all,

On Thu, 11 Jan 2024 17:44:57 -0800 Suren Baghdasaryan <surenb@google.com> wrote:
>
> I posted a quick fix for this issue here:
> https://lore.kernel.org/all/20240112013935.1474648-1-surenb@google.com/
> It cleanly applies over linux-next, mm-stable and mm-unstable. Andrew,
> Stephen, could you please pull the fix into your branches?

Since I will be away for a few days, I have applied that to linux-next today.

-- 
Cheers,
Stephen Rothwell

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