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Subject[syzbot] possible deadlock in fuse_reverse_inval_entry
From
Hello,

syzbot found the following issue on:

HEAD commit: 85a90500f9a1 Merge tag 'io_uring-5.14-2021-08-07' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10bc00c2300000
kernel config: https://syzkaller.appspot.com/x/.config?x=343fd21f6f4da2d6
dashboard link: https://syzkaller.appspot.com/bug?extid=9f747458f5990eaa8d43
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1427c9aa300000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1540a2f6300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9f747458f5990eaa8d43@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
5.14.0-rc4-syzkaller #0 Not tainted
--------------------------------------------
syz-executor799/8433 is trying to acquire lock:
ffff888039930ed0 (&type->i_mutex_dir_key#7){++++}-{3:3}, at: inode_lock include/linux/fs.h:774 [inline]
ffff888039930ed0 (&type->i_mutex_dir_key#7){++++}-{3:3}, at: fuse_reverse_inval_entry+0x1f5/0x530 fs/fuse/dir.c:1093

but task is already holding lock:
ffff888039930150 (&type->i_mutex_dir_key#7){++++}-{3:3}, at: inode_lock include/linux/fs.h:774 [inline]
ffff888039930150 (&type->i_mutex_dir_key#7){++++}-{3:3}, at: fuse_reverse_inval_entry+0x4c/0x530 fs/fuse/dir.c:1074

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

CPU0
----
lock(&type->i_mutex_dir_key#7);
lock(&type->i_mutex_dir_key#7);

*** DEADLOCK ***

May be due to missing lock nesting notation

2 locks held by syz-executor799/8433:
#0: ffff888022b6bb38 (&fc->killsb){.+.+}-{3:3}, at: fuse_notify_delete fs/fuse/dev.c:1540 [inline]
#0: ffff888022b6bb38 (&fc->killsb){.+.+}-{3:3}, at: fuse_notify fs/fuse/dev.c:1790 [inline]
#0: ffff888022b6bb38 (&fc->killsb){.+.+}-{3:3}, at: fuse_dev_do_write+0x285f/0x2bd0 fs/fuse/dev.c:1865
#1: ffff888039930150 (&type->i_mutex_dir_key#7){++++}-{3:3}, at: inode_lock include/linux/fs.h:774 [inline]
#1: ffff888039930150 (&type->i_mutex_dir_key#7){++++}-{3:3}, at: fuse_reverse_inval_entry+0x4c/0x530 fs/fuse/dir.c:1074

stack backtrace:
CPU: 1 PID: 8433 Comm: syz-executor799 Not tainted 5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
print_deadlock_bug kernel/locking/lockdep.c:2944 [inline]
check_deadlock kernel/locking/lockdep.c:2987 [inline]
validate_chain kernel/locking/lockdep.c:3776 [inline]
__lock_acquire.cold+0x149/0x3ab kernel/locking/lockdep.c:5015
lock_acquire kernel/locking/lockdep.c:5625 [inline]
lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
down_write+0x92/0x150 kernel/locking/rwsem.c:1406
inode_lock include/linux/fs.h:774 [inline]
fuse_reverse_inval_entry+0x1f5/0x530 fs/fuse/dir.c:1093
fuse_notify_delete fs/fuse/dev.c:1541 [inline]
fuse_notify fs/fuse/dev.c:1790 [inline]
fuse_dev_do_write+0x287f/0x2bd0 fs/fuse/dev.c:1865
fuse_dev_write+0x144/0x1d0 fs/fuse/dev.c:1949
call_write_iter include/linux/fs.h:2114 [inline]
new_sync_write+0x426/0x650 fs/read_write.c:518
vfs_write+0x75a/0xa40 fs/read_write.c:605
ksys_write+0x12d/0x250 fs/read_write.c:658
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4455e9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 81 14 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f64ac9752f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000004ce4e0 RCX: 00000000004455e9
RDX: 000000000000002e RSI: 00000000200000c0 RDI: 0000000000000003


---
This report 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 issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

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