[syzbot] [perf?] possible deadlock in refcount_dec_and_mutex_lock (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5ee8dbf54602 Merge tag 'fsverity-for-linus' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=101d5b5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5c49ee0942d1cdb
dashboard link: https://syzkaller.appspot.com/bug?extid=196a82fd904572696b3c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11b888ba580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12f758d6580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-5ee8dbf5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3cd4daffdac9/vmlinux-5ee8dbf5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7a6fec327094/bzImage-5ee8dbf5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+196a82...@syzkaller.appspotmail.com

R10: 0000000000000013 R11: 0000000000000246 R12: 0000000000000002
R13: 00007ff784215fac R14: 00007ff784215fa0 R15: 00007ff784215fa0
</TASK>
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.17/5460 is trying to acquire lock:
ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: refcount_dec_and_mutex_lock+0x30/0xa0 lib/refcount.c:118

but task is already holding lock:
ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: perf_mmap+0x1bb/0x4b0 kernel/events/core.c:7453

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&event->mmap_mutex);
lock(&event->mmap_mutex);

*** DEADLOCK ***

May be due to missing lock nesting notation

2 locks held by syz.0.17/5460:
#0: ffff888011a94080 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
#0: ffff888011a94080 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x234/0x4f0 mm/util.c:579
#1: ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
#1: ffff88801f26c9e0 (&event->mmap_mutex){+.+.}-{4:4}, at: perf_mmap+0x1bb/0x4b0 kernel/events/core.c:7453

stack backtrace:
CPU: 0 UID: 0 PID: 5460 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
check_deadlock kernel/locking/lockdep.c:3093 [inline]
validate_chain kernel/locking/lockdep.c:3895 [inline]
__lock_acquire+0x253f/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/mutex.c:614 [inline]
__mutex_lock+0x19f/0x1300 kernel/locking/mutex.c:776
refcount_dec_and_mutex_lock+0x30/0xa0 lib/refcount.c:118
perf_mmap_close+0x953/0xf90 kernel/events/core.c:7064
perf_mmap+0x418/0x4b0 kernel/events/core.c:7488
vfs_mmap include/linux/fs.h:2070 [inline]
mmap_file mm/internal.h:167 [inline]
__mmap_new_file_vma mm/vma.c:2468 [inline]
__mmap_new_vma mm/vma.c:2532 [inline]
__mmap_region mm/vma.c:2759 [inline]
mmap_region+0x18fe/0x2240 mm/vma.c:2837
do_mmap+0xc39/0x10c0 mm/mmap.c:559
vm_mmap_pgoff+0x2c9/0x4f0 mm/util.c:581
ksys_mmap_pgoff+0x51e/0x760 mm/mmap.c:605
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff783f9c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeef4c8518 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007ff784215fa0 RCX: 00007ff783f9c799
RDX: 0000000001000008 RSI: 0000000000002000 RDI: 0000200000ffe000
RBP: 00007ffeef4c8580 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000000013 R11: 0000000000000246 R12: 0000000000000002
R13: 00007ff784215fac R14: 00007ff784215fa0 R15: 00007ff784215fa0
</TASK>


---
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[Tetsuo Handa]

Side effect of commit 77de62ad3de3 ("perf/core: Fix refcount bug and potential UAF in perf_mmap").