From: syzbot ci <syzbot+cicf36371c0f59f4ad@syzkaller.appspotmail.com>
To: akpm@linux-foundation.org, chriscli@google.com, jannh@google.com,
liam.howlett@oracle.com, linux-mm@kvack.org,
lorenzo.stoakes@oracle.com, pfalcato@suse.de,
shakeel.butt@linux.dev, surenb@google.com, vbabka@suse.cz,
willy@infradead.org
Cc: syzbot@lists.linux.dev, syzkaller-bugs@googlegroups.com
Subject: [syzbot ci] Re: vma_start_write_killable
Date: Tue, 04 Nov 2025 01:08:52 -0800 [thread overview]
Message-ID: <6909c2a4.050a0220.98a6.00a8.GAE@google.com> (raw)
In-Reply-To: <20251103180348.3368668-1-willy@infradead.org>
syzbot ci has tested the following series
[v1] vma_start_write_killable
https://lore.kernel.org/all/20251103180348.3368668-1-willy@infradead.org
* [PATCH 1/2] mm: Add vma_start_write_killable()
* [PATCH 2/2] mm: Use vma_start_write_killable() in dup_mmap()
and found the following issue:
possible deadlock in exit_mmap
Full report is available here:
https://ci.syzbot.org/series/3eb0eeab-3254-43ec-ad2d-e439ab81ad3e
***
possible deadlock in exit_mmap
tree: torvalds
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base: fd57572253bc356330dbe5b233c2e1d8426c66fd
arch: amd64
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config: https://ci.syzbot.org/builds/b55422d4-9fe5-4a2c-9938-3e67223a358f/config
C repro: https://ci.syzbot.org/findings/ecb8b9e5-1c01-48c4-b7b6-9155dea27118/c_repro
syz repro: https://ci.syzbot.org/findings/ecb8b9e5-1c01-48c4-b7b6-9155dea27118/syz_repro
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.24/6004 is trying to acquire lock:
ffff88810f7fcd20 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock include/linux/mmap_lock.h:395 [inline]
ffff88810f7fcd20 (&mm->mmap_lock){++++}-{4:4}, at: exit_mmap+0x126/0xb40 mm/mmap.c:1265
but task is already holding lock:
ffff888111ad0f88 (vm_lock){++++}-{0:0}, at: __vma_start_write+0x23/0x140 mm/mmap_lock.c:92
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (vm_lock){++++}-{0:0}:
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
__vma_enter_locked+0x1a0/0x570 mm/mmap_lock.c:65
__vma_start_write+0x23/0x140 mm/mmap_lock.c:92
vma_start_write include/linux/mmap_lock.h:213 [inline]
mprotect_fixup+0x57d/0x9c0 mm/mprotect.c:828
setup_arg_pages+0x52a/0xa90 fs/exec.c:670
load_elf_binary+0xba4/0x2740 fs/binfmt_elf.c:1028
search_binary_handler fs/exec.c:1670 [inline]
exec_binprm fs/exec.c:1702 [inline]
bprm_execve+0x99c/0x1450 fs/exec.c:1754
kernel_execve+0x8f0/0x9f0 fs/exec.c:1920
try_to_run_init_process+0x13/0x60 init/main.c:1411
kernel_init+0xad/0x1d0 init/main.c:1539
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #0 (&mm->mmap_lock){++++}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537
mmap_read_lock include/linux/mmap_lock.h:395 [inline]
exit_mmap+0x126/0xb40 mm/mmap.c:1265
__mmput+0x118/0x430 kernel/fork.c:1133
mmput kernel/fork.c:1156 [inline]
dup_mm kernel/fork.c:1506 [inline]
copy_mm+0x1f3/0x4b0 kernel/fork.c:1541
copy_process+0x1706/0x3c00 kernel/fork.c:2181
kernel_clone+0x21e/0x840 kernel/fork.c:2609
__do_sys_clone kernel/fork.c:2750 [inline]
__se_sys_clone kernel/fork.c:2734 [inline]
__x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2734
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(vm_lock);
lock(&mm->mmap_lock);
lock(vm_lock);
rlock(&mm->mmap_lock);
*** DEADLOCK ***
2 locks held by syz.0.24/6004:
#0: ffffffff8dff64d0 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mm kernel/fork.c:1488 [inline]
#0: ffffffff8dff64d0 (dup_mmap_sem){.+.+}-{0:0}, at: copy_mm+0x131/0x4b0 kernel/fork.c:1541
#1: ffff888111ad0f88 (vm_lock){++++}-{0:0}, at: __vma_start_write+0x23/0x140 mm/mmap_lock.c:92
stack backtrace:
CPU: 0 UID: 0 PID: 6004 Comm: syz.0.24 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537
mmap_read_lock include/linux/mmap_lock.h:395 [inline]
exit_mmap+0x126/0xb40 mm/mmap.c:1265
__mmput+0x118/0x430 kernel/fork.c:1133
mmput kernel/fork.c:1156 [inline]
dup_mm kernel/fork.c:1506 [inline]
copy_mm+0x1f3/0x4b0 kernel/fork.c:1541
copy_process+0x1706/0x3c00 kernel/fork.c:2181
kernel_clone+0x21e/0x840 kernel/fork.c:2609
__do_sys_clone kernel/fork.c:2750 [inline]
__se_sys_clone kernel/fork.c:2734 [inline]
__x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2734
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f45ab18efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f45abfaefe8 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f45ab3e6090 RCX: 00007f45ab18efc9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000001000
RBP: 00007f45ab211f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f45ab3e6128 R14: 00007f45ab3e6090 R15: 00007ffe9b2a02c8
</TASK>
------------[ cut here ]------------
refcount_t: saturated; leaking memory.
WARNING: CPU: 0 PID: 6004 at lib/refcount.c:19 refcount_warn_saturate+0x13a/0x1d0 lib/refcount.c:19
Modules linked in:
CPU: 0 UID: 0 PID: 6004 Comm: syz.0.24 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x13a/0x1d0 lib/refcount.c:19
Code: 20 57 be 8b e8 87 a8 f9 fc 90 0f 0b 90 90 eb b7 e8 6b 8c 36 fd c6 05 1b 75 dd 0a 01 90 48 c7 c7 60 56 be 8b e8 67 a8 f9 fc 90 <0f> 0b 90 90 eb 97 e8 4b 8c 36 fd c6 05 ff 74 dd 0a 01 90 48 c7 c7
RSP: 0018:ffffc900036f75a8 EFLAGS: 00010246
RAX: 37ca69179b3b1c00 RBX: 0000000000000000 RCX: ffff88810c6c0000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: ffffc900036f76b0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1bba650 R12: ffff888111ad0f80
R13: 1ffff920006deec4 R14: ffff888111ad0f80 R15: 0000000000000000
FS: 00007f45abfaf6c0(0000) GS:ffff88818eb3e000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f45abfaefc8 CR3: 00000001bbaba000 CR4: 00000000000006f0
Call Trace:
<TASK>
__refcount_add_not_zero include/linux/refcount.h:187 [inline]
refcount_add_not_zero include/linux/refcount.h:212 [inline]
__vma_enter_locked+0x534/0x570 mm/mmap_lock.c:62
__vma_start_write+0x23/0x140 mm/mmap_lock.c:92
vma_start_write include/linux/mmap_lock.h:213 [inline]
vma_merge_existing_range mm/vma.c:905 [inline]
vma_modify+0xce0/0x1970 mm/vma.c:1608
vma_modify_flags_uffd+0x204/0x250 mm/vma.c:1697
userfaultfd_clear_vma mm/userfaultfd.c:2030 [inline]
userfaultfd_release_all+0x34c/0x5d0 mm/userfaultfd.c:2149
userfaultfd_release+0xe7/0x1b0 fs/userfaultfd.c:868
__fput+0x44c/0xa70 fs/file_table.c:468
task_work_run+0x1d4/0x260 kernel/task_work.c:227
get_signal+0x11ec/0x1340 kernel/signal.c:2807
arch_do_signal_or_restart+0xa0/0x790 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x72/0x130 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x2bd/0xfa0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f45ab18efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f45abfaefe8 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: fffffffffffffff4 RBX: 00007f45ab3e6090 RCX: 00007f45ab18efc9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000001000
RBP: 00007f45ab211f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f45ab3e6128 R14: 00007f45ab3e6090 R15: 00007ffe9b2a02c8
</TASK>
***
If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syzbot@syzkaller.appspotmail.com
---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.
prev parent reply other threads:[~2025-11-04 9:08 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-03 18:03 [PATCH 0/2] vma_start_write_killable Matthew Wilcox (Oracle)
2025-11-03 18:03 ` [PATCH 1/2] mm: Add vma_start_write_killable() Matthew Wilcox (Oracle)
2025-11-03 21:53 ` Suren Baghdasaryan
2025-11-03 23:14 ` Matthew Wilcox
2025-11-03 23:17 ` Suren Baghdasaryan
2025-11-04 16:09 ` Matthew Wilcox
2025-11-07 19:12 ` Liam R. Howlett
2025-11-03 18:03 ` [PATCH 2/2] mm: Use vma_start_write_killable() in dup_mmap() Matthew Wilcox (Oracle)
2025-11-03 21:56 ` Suren Baghdasaryan
2025-11-07 19:12 ` Liam R. Howlett
2025-11-04 9:08 ` syzbot ci [this message]
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