Re: [syzbot] [mm?] possible deadlock in lock_next_vma

[syzbot <syzbot+159a3ef1894076a6a6e9@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    0be23810e32e Add linux-next specific files for 20250714
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15cfb0f0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=be9e2082003f81ff
dashboard link: https://syzkaller.appspot.com/bug?extid=159a3ef1894076a6a6e9
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1003b18c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11437d82580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/69e6cc49d526/disk-0be23810.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/71d1bab88eaa/vmlinux-0be23810.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5a516dc7bb0d/bzImage-0be23810.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+159a3ef1894076a6a6e9@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc6-next-20250714-syzkaller #0 Not tainted
------------------------------------------------------
syz.2.103/6308 is trying to acquire lock:
ffff88807d33bde0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable include/linux/mmap_lock.h:432 [inline]
ffff88807d33bde0 (&mm->mmap_lock){++++}-{4:4}, at: lock_vma_under_mmap_lock mm/mmap_lock.c:189 [inline]
ffff88807d33bde0 (&mm->mmap_lock){++++}-{4:4}, at: lock_next_vma+0x802/0xdc0 mm/mmap_lock.c:264

but task is already holding lock:
ffff8880338c6948 (vm_lock){++++}-{0:0}, at: lock_next_vma+0x146/0xdc0 mm/mmap_lock.c:220

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:5871
       __vma_enter_locked+0x182/0x380 mm/mmap_lock.c:63
       __vma_start_write+0x1e/0x120 mm/mmap_lock.c:87
       vma_start_write include/linux/mmap_lock.h:267 [inline]
       mprotect_fixup+0x571/0x9b0 mm/mprotect.c:670
       setup_arg_pages+0x53a/0xaa0 fs/exec.c:670
       load_elf_binary+0xb9f/0x2730 fs/binfmt_elf.c:1013
       search_binary_handler fs/exec.c:1670 [inline]
       exec_binprm fs/exec.c:1702 [inline]
       bprm_execve+0x999/0x1450 fs/exec.c:1754
       kernel_execve+0x8f0/0x9f0 fs/exec.c:1920
       try_to_run_init_process+0x13/0x60 init/main.c:1397
       kernel_init+0xad/0x1d0 init/main.c:1525
       ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
       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:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1562
       mmap_read_lock_killable include/linux/mmap_lock.h:432 [inline]
       lock_vma_under_mmap_lock mm/mmap_lock.c:189 [inline]
       lock_next_vma+0x802/0xdc0 mm/mmap_lock.c:264
       get_next_vma fs/proc/task_mmu.c:182 [inline]
       query_vma_find_by_addr fs/proc/task_mmu.c:512 [inline]
       query_matching_vma+0x319/0x5c0 fs/proc/task_mmu.c:544
       do_procmap_query fs/proc/task_mmu.c:629 [inline]
       procfs_procmap_ioctl+0x3f9/0xd50 fs/proc/task_mmu.c:747
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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
       ----                    ----
  rlock(vm_lock);
                               lock(&mm->mmap_lock);
                               lock(vm_lock);
  rlock(&mm->mmap_lock);

 *** DEADLOCK ***

1 lock held by syz.2.103/6308:
 #0: ffff8880338c6948 (vm_lock){++++}-{0:0}, at: lock_next_vma+0x146/0xdc0 mm/mmap_lock.c:220

stack backtrace:
CPU: 0 UID: 0 PID: 6308 Comm: syz.2.103 Not tainted 6.16.0-rc6-next-20250714-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1562
 mmap_read_lock_killable include/linux/mmap_lock.h:432 [inline]
 lock_vma_under_mmap_lock mm/mmap_lock.c:189 [inline]
 lock_next_vma+0x802/0xdc0 mm/mmap_lock.c:264
 get_next_vma fs/proc/task_mmu.c:182 [inline]
 query_vma_find_by_addr fs/proc/task_mmu.c:512 [inline]
 query_matching_vma+0x319/0x5c0 fs/proc/task_mmu.c:544
 do_procmap_query fs/proc/task_mmu.c:629 [inline]
 procfs_procmap_ioctl+0x3f9/0xd50 fs/proc/task_mmu.c:747
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa51ab8e929
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:00007fa51b99b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fa51adb5fa0 RCX: 00007fa51ab8e929
RDX: 0000200000000180 RSI: 00000000c0686611 RDI: 0000000000000003
RBP: 00007fa51ac10b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fa51adb5fa0 R15: 00007ffdecbd3a88
 </TASK>


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