[syzbot] [mm?] possible deadlock in lock_vma

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ae00c445390b Add linux-next specific files for 20240212
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=17478592180000
kernel config: https://syzkaller.appspot.com/x/.config?x=4eb3a27eddb32a14
dashboard link: https://syzkaller.appspot.com/bug?extid=27f783f9d240834c9d44
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17406e42180000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=111cb500180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8b2a2d0b511f/disk-ae00c445.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a668a09c9d03/vmlinux-ae00c445.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4ad623928692/bzImage-ae00c445.xz

The issue was bisected to:

commit 31d97016c80a83daa4c938014c81282810a14773
Author: Lokesh Gidra <lokes...@google.com>
Date: Thu Feb 8 21:22:04 2024 +0000

userfaultfd: use per-vma locks in userfaultfd operations

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=129ff100180000
final oops: https://syzkaller.appspot.com/x/report.txt?x=119ff100180000
console output: https://syzkaller.appspot.com/x/log.txt?x=169ff100180000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+27f783...@syzkaller.appspotmail.com
Fixes: 31d97016c80a ("userfaultfd: use per-vma locks in userfaultfd operations")

======================================================
WARNING: possible circular locking dependency detected
6.8.0-rc4-next-20240212-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor800/5064 is trying to acquire lock:
ffff888021d401a0 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_lock include/linux/mmap_lock.h:146 [inline]
ffff888021d401a0 (&mm->mmap_lock){++++}-{3:3}, at: lock_vma+0xc5/0x260 mm/userfaultfd.c:73

but task is already holding lock:
ffff88802b989730 (&vma->vm_lock->lock){++++}-{3:3}, at: lock_vma+0x1a1/0x260 mm/userfaultfd.c:87

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&vma->vm_lock->lock){++++}-{3:3}:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
down_write+0x3a/0x50 kernel/locking/rwsem.c:1579
vma_start_write include/linux/mm.h:716 [inline]
vma_link+0x2c6/0x550 mm/mmap.c:416
insert_vm_struct+0x1a3/0x260 mm/mmap.c:3331
__bprm_mm_init fs/exec.c:282 [inline]
bprm_mm_init fs/exec.c:384 [inline]
alloc_bprm+0x543/0xa00 fs/exec.c:1579
kernel_execve+0x99/0xa10 fs/exec.c:2008
try_to_run_init_process init/main.c:1361 [inline]
kernel_init+0xe8/0x2b0 init/main.c:1488
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:242

-> #0 (&mm->mmap_lock){++++}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
down_read+0xb1/0xa40 kernel/locking/rwsem.c:1526
mmap_read_lock include/linux/mmap_lock.h:146 [inline]
lock_vma+0xc5/0x260 mm/userfaultfd.c:73
find_and_lock_vmas mm/userfaultfd.c:1405 [inline]
move_pages+0x18c/0xff0 mm/userfaultfd.c:1546
userfaultfd_move fs/userfaultfd.c:2008 [inline]
userfaultfd_ioctl+0x5c10/0x72c0 fs/userfaultfd.c:2126
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:857
do_syscall_64+0xfb/0x240
entry_SYSCALL_64_after_hwframe+0x6d/0x75

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(&vma->vm_lock->lock);
lock(&mm->mmap_lock);
lock(&vma->vm_lock->lock);
rlock(&mm->mmap_lock);

*** DEADLOCK ***

1 lock held by syz-executor800/5064:
#0: ffff88802b989730 (&vma->vm_lock->lock){++++}-{3:3}, at: lock_vma+0x1a1/0x260 mm/userfaultfd.c:87

stack backtrace:
CPU: 1 PID: 5064 Comm: syz-executor800 Not tainted 6.8.0-rc4-next-20240212-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
down_read+0xb1/0xa40 kernel/locking/rwsem.c:1526
mmap_read_lock include/linux/mmap_lock.h:146 [inline]
lock_vma+0xc5/0x260 mm/userfaultfd.c:73
find_and_lock_vmas mm/userfaultfd.c:1405 [inline]
move_pages+0x18c/0xff0 mm/userfaultfd.c:1546
userfaultfd_move fs/userfaultfd.c:2008 [inline]
userfaultfd_ioctl+0x5c10/0x72c0 fs/userfaultfd.c:2126
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:857
do_syscall_64+0xfb/0x240
entry_SYSCALL_64_after_hwframe+0x6d/0x75
RIP: 0033:0x7f86fc35f329
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:00007ffd53428e38 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffd53429008 RCX: 00007f86fc35f329
RDX: 0000000020000040 RSI: 00000000c028aa05 RDI:


---
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