possible deadlock in proc_pid_stack (2)

From: syzbot
Date: Thu Aug 27 2020 - 23:18:36 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 494d311a Add linux-next specific files for 20200821
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1644d50e900000
kernel config: https://syzkaller.appspot.com/x/.config?x=a61d44f28687f508
dashboard link: https://syzkaller.appspot.com/bug?extid=a26ada9907073b2f6f97
compiler: gcc (GCC) 10.1.0-syz 20200507

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a26ada9907073b2f6f97@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc1-next-20200821-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.2/26207 is trying to acquire lock:
ffff8880a064e688 (&sig->exec_update_mutex){+.+.}-{3:3}, at: lock_trace fs/proc/base.c:408 [inline]
ffff8880a064e688 (&sig->exec_update_mutex){+.+.}-{3:3}, at: proc_pid_stack+0xf0/0x2a0 fs/proc/base.c:452

but task is already holding lock:
ffff88809dc4d8f8 (&p->lock){+.+.}-{3:3}, at: seq_read+0x61/0x1070 fs/seq_file.c:155

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&p->lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:956 [inline]
__mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
seq_read+0x61/0x1070 fs/seq_file.c:155
do_loop_readv_writev fs/read_write.c:734 [inline]
do_loop_readv_writev fs/read_write.c:721 [inline]
do_iter_read+0x48e/0x6e0 fs/read_write.c:955
vfs_readv+0xe5/0x150 fs/read_write.c:1073
kernel_readv fs/splice.c:355 [inline]
default_file_splice_read.constprop.0+0x4e6/0x9e0 fs/splice.c:412
do_splice_to+0x137/0x170 fs/splice.c:871
splice_direct_to_actor+0x307/0x980 fs/splice.c:950
do_splice_direct+0x1b3/0x280 fs/splice.c:1059
do_sendfile+0x55f/0xd40 fs/read_write.c:1540
__do_sys_sendfile64 fs/read_write.c:1601 [inline]
__se_sys_sendfile64 fs/read_write.c:1587 [inline]
__x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1587
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #2 (sb_writers#4){.+.+}-{0:0}:
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write+0x234/0x470 fs/super.c:1672
sb_start_write include/linux/fs.h:1643 [inline]
mnt_want_write+0x3a/0xb0 fs/namespace.c:354
ovl_do_remove+0xe1/0xe00 fs/overlayfs/dir.c:889
vfs_rmdir.part.0+0x113/0x430 fs/namei.c:3712
vfs_rmdir fs/namei.c:3698 [inline]
do_rmdir+0x3ae/0x440 fs/namei.c:3773
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #1 (&ovl_i_mutex_dir_key[depth]#2){++++}-{3:3}:
down_read+0x96/0x420 kernel/locking/rwsem.c:1492
inode_lock_shared include/linux/fs.h:789 [inline]
lookup_slow fs/namei.c:1560 [inline]
walk_component+0x409/0x6a0 fs/namei.c:1860
lookup_last fs/namei.c:2309 [inline]
path_lookupat+0x1ba/0x830 fs/namei.c:2333
filename_lookup+0x19f/0x560 fs/namei.c:2366
create_local_trace_uprobe+0x87/0x4e0 kernel/trace/trace_uprobe.c:1574
perf_uprobe_init+0x132/0x210 kernel/trace/trace_event_perf.c:323
perf_uprobe_event_init+0xff/0x1c0 kernel/events/core.c:9608
perf_try_init_event+0x12a/0x560 kernel/events/core.c:10927
perf_init_event kernel/events/core.c:10979 [inline]
perf_event_alloc.part.0+0xe04/0x3790 kernel/events/core.c:11257
perf_event_alloc kernel/events/core.c:11636 [inline]
__do_sys_perf_event_open+0x72c/0x2cb0 kernel/events/core.c:11752
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #0 (&sig->exec_update_mutex){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x2a6b/0x5640 kernel/locking/lockdep.c:4426
lock_acquire+0x1f1/0xad0 kernel/locking/lockdep.c:5005
__mutex_lock_common kernel/locking/mutex.c:956 [inline]
__mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
lock_trace fs/proc/base.c:408 [inline]
proc_pid_stack+0xf0/0x2a0 fs/proc/base.c:452
proc_single_show+0x116/0x1e0 fs/proc/base.c:775
seq_read+0x432/0x1070 fs/seq_file.c:208
do_loop_readv_writev fs/read_write.c:734 [inline]
do_loop_readv_writev fs/read_write.c:721 [inline]
do_iter_read+0x48e/0x6e0 fs/read_write.c:955
vfs_readv+0xe5/0x150 fs/read_write.c:1073
do_preadv fs/read_write.c:1165 [inline]
__do_sys_preadv fs/read_write.c:1215 [inline]
__se_sys_preadv fs/read_write.c:1210 [inline]
__x64_sys_preadv+0x231/0x310 fs/read_write.c:1210
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

other info that might help us debug this:

Chain exists of:
&sig->exec_update_mutex --> sb_writers#4 --> &p->lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&p->lock);
lock(sb_writers#4);
lock(&p->lock);
lock(&sig->exec_update_mutex);

*** DEADLOCK ***

1 lock held by syz-executor.2/26207:
#0: ffff88809dc4d8f8 (&p->lock){+.+.}-{3:3}, at: seq_read+0x61/0x1070 fs/seq_file.c:155

stack backtrace:
CPU: 1 PID: 26207 Comm: syz-executor.2 Not tainted 5.9.0-rc1-next-20200821-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+0x18f/0x20d lib/dump_stack.c:118
check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x2a6b/0x5640 kernel/locking/lockdep.c:4426
lock_acquire+0x1f1/0xad0 kernel/locking/lockdep.c:5005
__mutex_lock_common kernel/locking/mutex.c:956 [inline]
__mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
lock_trace fs/proc/base.c:408 [inline]
proc_pid_stack+0xf0/0x2a0 fs/proc/base.c:452
proc_single_show+0x116/0x1e0 fs/proc/base.c:775
seq_read+0x432/0x1070 fs/seq_file.c:208
do_loop_readv_writev fs/read_write.c:734 [inline]
do_loop_readv_writev fs/read_write.c:721 [inline]
do_iter_read+0x48e/0x6e0 fs/read_write.c:955
vfs_readv+0xe5/0x150 fs/read_write.c:1073
do_preadv fs/read_write.c:1165 [inline]
__do_sys_preadv fs/read_write.c:1215 [inline]
__se_sys_preadv fs/read_write.c:1210 [inline]
__x64_sys_preadv+0x231/0x310 fs/read_write.c:1210
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d579
Code: 5d b4 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 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f3c7522cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 0000000000025780 RCX: 000000000045d579
RDX: 00000000000002bf RSI: 00000000200017c0 RDI: 0000000000000003
RBP: 000000000118cf90 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007ffe544c9bff R14: 00007f3c7522d9c0 R15: 000000000118cf4c

---
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Next message: Muchun Song: "[PATCH v2] mm/hugetlb: Fix a race between hugetlb sysctl handlers"
Previous message: Jens Axboe: "Re: [PATCH v6 0/3] io_uring: add restrictions to support untrusted applications and guests"
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