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Subjectpossible deadlock in walk_component
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Hello,

syzbot found the following crash on:

HEAD commit: 63623fd4 Merge tag 'for-linus' of git://git.kernel.org/pub..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=173a3529e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=5d2e033af114153f
dashboard link: https://syzkaller.appspot.com/bug?extid=a84f8e843059b8bb50c3
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a84f8e843059b8bb50c3@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.6.0-rc3-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.3/1694 is trying to acquire lock:
ffff888025e9e220 (&ovl_i_mutex_dir_key[depth]){++++}, at: inode_lock_shared include/linux/fs.h:801 [inline]
ffff888025e9e220 (&ovl_i_mutex_dir_key[depth]){++++}, at: lookup_slow fs/namei.c:1773 [inline]
ffff888025e9e220 (&ovl_i_mutex_dir_key[depth]){++++}, at: walk_component+0x2c2/0x5f0 fs/namei.c:1915

but task is already holding lock:
ffff88808c28e750 (&sig->cred_guard_mutex){+.+.}, at: __do_sys_perf_event_open kernel/events/core.c:11266 [inline]
ffff88808c28e750 (&sig->cred_guard_mutex){+.+.}, at: __se_sys_perf_event_open+0xb50/0x4140 kernel/events/core.c:11160

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&sig->cred_guard_mutex){+.+.}:
lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484
__mutex_lock_common+0x16e/0x2f30 kernel/locking/mutex.c:956
__mutex_lock kernel/locking/mutex.c:1103 [inline]
mutex_lock_killable_nested+0x1b/0x30 kernel/locking/mutex.c:1133
lock_trace fs/proc/base.c:408 [inline]
proc_pid_stack+0xd9/0x200 fs/proc/base.c:452
proc_single_show+0xe7/0x180 fs/proc/base.c:758
seq_read+0x4d8/0xdb0 fs/seq_file.c:229
do_loop_readv_writev fs/read_write.c:714 [inline]
do_iter_read+0x4a2/0x5b0 fs/read_write.c:935
vfs_readv+0xc2/0x120 fs/read_write.c:1053
kernel_readv fs/splice.c:365 [inline]
default_file_splice_read+0x579/0xa40 fs/splice.c:422
do_splice_to fs/splice.c:892 [inline]
splice_direct_to_actor+0x3c9/0xb90 fs/splice.c:971
do_splice_direct+0x200/0x330 fs/splice.c:1080
do_sendfile+0x7e4/0xfd0 fs/read_write.c:1520
__do_sys_sendfile64 fs/read_write.c:1581 [inline]
__se_sys_sendfile64 fs/read_write.c:1567 [inline]
__x64_sys_sendfile64+0x176/0x1b0 fs/read_write.c:1567
do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (&p->lock){+.+.}:
lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484
__mutex_lock_common+0x16e/0x2f30 kernel/locking/mutex.c:956
__mutex_lock kernel/locking/mutex.c:1103 [inline]
mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1118
seq_read+0x6b/0xdb0 fs/seq_file.c:161
proc_reg_read+0x1d5/0x2e0 fs/proc/inode.c:223
do_loop_readv_writev fs/read_write.c:714 [inline]
do_iter_read+0x4a2/0x5b0 fs/read_write.c:935
vfs_readv+0xc2/0x120 fs/read_write.c:1053
kernel_readv fs/splice.c:365 [inline]
default_file_splice_read+0x579/0xa40 fs/splice.c:422
do_splice_to fs/splice.c:892 [inline]
splice_direct_to_actor+0x3c9/0xb90 fs/splice.c:971
do_splice_direct+0x200/0x330 fs/splice.c:1080
do_sendfile+0x7e4/0xfd0 fs/read_write.c:1520
__do_sys_sendfile64 fs/read_write.c:1581 [inline]
__se_sys_sendfile64 fs/read_write.c:1567 [inline]
__x64_sys_sendfile64+0x176/0x1b0 fs/read_write.c:1567
do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (sb_writers#3){.+.+}:
lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484
percpu_down_read include/linux/percpu-rwsem.h:40 [inline]
__sb_start_write+0x189/0x420 fs/super.c:1674
sb_start_write include/linux/fs.h:1649 [inline]
mnt_want_write+0x4a/0xa0 fs/namespace.c:354
ovl_want_write+0x77/0x80 fs/overlayfs/util.c:21
ovl_create_object+0xaf/0x2d0 fs/overlayfs/dir.c:596
ovl_create+0x29/0x30 fs/overlayfs/dir.c:627
lookup_open fs/namei.c:3309 [inline]
do_last fs/namei.c:3401 [inline]
path_openat+0x230c/0x4380 fs/namei.c:3607
do_filp_open+0x192/0x3d0 fs/namei.c:3637
do_sys_openat2+0x42b/0x6f0 fs/open.c:1149
do_sys_open fs/open.c:1165 [inline]
__do_sys_openat fs/open.c:1179 [inline]
__se_sys_openat fs/open.c:1174 [inline]
__x64_sys_openat+0x1e6/0x210 fs/open.c:1174
do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&ovl_i_mutex_dir_key[depth]){++++}:
check_prev_add kernel/locking/lockdep.c:2475 [inline]
check_prevs_add kernel/locking/lockdep.c:2580 [inline]
validate_chain+0x1507/0x7be0 kernel/locking/lockdep.c:2970
__lock_acquire+0xc5a/0x1bc0 kernel/locking/lockdep.c:3954
lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484
down_read+0x39/0x50 kernel/locking/rwsem.c:1495
inode_lock_shared include/linux/fs.h:801 [inline]
lookup_slow fs/namei.c:1773 [inline]
walk_component+0x2c2/0x5f0 fs/namei.c:1915
lookup_last fs/namei.c:2391 [inline]
path_lookupat+0x19f/0x680 fs/namei.c:2436
filename_lookup+0x1d4/0x690 fs/namei.c:2466
kern_path+0x35/0x40 fs/namei.c:2552
create_local_trace_uprobe+0x40/0x610 kernel/trace/trace_uprobe.c:1568
perf_uprobe_init+0x10c/0x1b0 kernel/trace/trace_event_perf.c:323
perf_uprobe_event_init+0xe0/0x170 kernel/events/core.c:9171
perf_try_init_event+0x14e/0x3c0 kernel/events/core.c:10471
perf_init_event kernel/events/core.c:10523 [inline]
perf_event_alloc+0x1032/0x2810 kernel/events/core.c:10803
__do_sys_perf_event_open kernel/events/core.c:11286 [inline]
__se_sys_perf_event_open+0x6cf/0x4140 kernel/events/core.c:11160
__x64_sys_perf_event_open+0xbf/0xd0 kernel/events/core.c:11160
do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
&ovl_i_mutex_dir_key[depth] --> &p->lock --> &sig->cred_guard_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&sig->cred_guard_mutex);
lock(&p->lock);
lock(&sig->cred_guard_mutex);
lock(&ovl_i_mutex_dir_key[depth]);

*** DEADLOCK ***

2 locks held by syz-executor.3/1694:
#0: ffff88808c28e750 (&sig->cred_guard_mutex){+.+.}, at: __do_sys_perf_event_open kernel/events/core.c:11266 [inline]
#0: ffff88808c28e750 (&sig->cred_guard_mutex){+.+.}, at: __se_sys_perf_event_open+0xb50/0x4140 kernel/events/core.c:11160
#1: ffffffff8a48b8f0 (&pmus_srcu){....}, at: rcu_lock_acquire+0xd/0x40 include/linux/rcupdate.h:208

stack backtrace:
CPU: 0 PID: 1694 Comm: syz-executor.3 Not tainted 5.6.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1fb/0x318 lib/dump_stack.c:118
print_circular_bug+0xc3f/0xe70 kernel/locking/lockdep.c:1684
check_noncircular+0x206/0x3a0 kernel/locking/lockdep.c:1808
check_prev_add kernel/locking/lockdep.c:2475 [inline]
check_prevs_add kernel/locking/lockdep.c:2580 [inline]
validate_chain+0x1507/0x7be0 kernel/locking/lockdep.c:2970
__lock_acquire+0xc5a/0x1bc0 kernel/locking/lockdep.c:3954
lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484
down_read+0x39/0x50 kernel/locking/rwsem.c:1495
inode_lock_shared include/linux/fs.h:801 [inline]
lookup_slow fs/namei.c:1773 [inline]
walk_component+0x2c2/0x5f0 fs/namei.c:1915
lookup_last fs/namei.c:2391 [inline]
path_lookupat+0x19f/0x680 fs/namei.c:2436
filename_lookup+0x1d4/0x690 fs/namei.c:2466
kern_path+0x35/0x40 fs/namei.c:2552
create_local_trace_uprobe+0x40/0x610 kernel/trace/trace_uprobe.c:1568
perf_uprobe_init+0x10c/0x1b0 kernel/trace/trace_event_perf.c:323
perf_uprobe_event_init+0xe0/0x170 kernel/events/core.c:9171
perf_try_init_event+0x14e/0x3c0 kernel/events/core.c:10471
perf_init_event kernel/events/core.c:10523 [inline]
perf_event_alloc+0x1032/0x2810 kernel/events/core.c:10803
__do_sys_perf_event_open kernel/events/core.c:11286 [inline]
__se_sys_perf_event_open+0x6cf/0x4140 kernel/events/core.c:11160
__x64_sys_perf_event_open+0xbf/0xd0 kernel/events/core.c:11160
do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c479
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f2bd4543c78 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: ffffffffffffffda RBX: 00007f2bd45446d4 RCX: 000000000045c479
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000180
RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000813 R14: 00000000004ca8bf R15: 000000000076bf2c


---
This bug 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 bug report. See:
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