Re: [syzbot] possible deadlock in p9_req_put

[syzbot <syzbot+50f7e8d06c3768dd97f3@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    ca688bff68bc Add linux-next specific files for 20220808
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1408148e080000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4c20e006003cdecb
dashboard link: https://syzkaller.appspot.com/bug?extid=50f7e8d06c3768dd97f3
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11f6ea66080000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1640de8e080000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+50f7e8d06c3768dd97f3@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
5.19.0-next-20220808-syzkaller #0 Not tainted
--------------------------------------------
kworker/1:2/1590 is trying to acquire lock:
ffff888079686c18 (&clnt->lock){+.+.}-{2:2}, at: p9_tag_remove net/9p/client.c:367 [inline]
ffff888079686c18 (&clnt->lock){+.+.}-{2:2}, at: p9_req_put net/9p/client.c:375 [inline]
ffff888079686c18 (&clnt->lock){+.+.}-{2:2}, at: p9_req_put+0xc6/0x250 net/9p/client.c:372

but task is already holding lock:
ffff888079686c18 (&clnt->lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:349 [inline]
ffff888079686c18 (&clnt->lock){+.+.}-{2:2}, at: p9_conn_cancel+0xaa/0x970 net/9p/trans_fd.c:192

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

       CPU0
       ----
  lock(&clnt->lock);
  lock(&clnt->lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by kworker/1:2/1590:
 #0: ffff888011864d38 ((wq_completion)events){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff888011864d38 ((wq_completion)events){+.+.}-{0:0}, at: arch_atomic_long_set include/linux/atomic/atomic-long.h:41 [inline]
 #0: ffff888011864d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic_long_set include/linux/atomic/atomic-instrumented.h:1280 [inline]
 #0: ffff888011864d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:636 [inline]
 #0: ffff888011864d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:663 [inline]
 #0: ffff888011864d38 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x87a/0x1610 kernel/workqueue.c:2260
 #1: ffffc90006357da8 (p9_poll_work){+.+.}-{0:0}, at: process_one_work+0x8ae/0x1610 kernel/workqueue.c:2264
 #2: ffff888079686c18 (&clnt->lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:349 [inline]
 #2: ffff888079686c18 (&clnt->lock){+.+.}-{2:2}, at: p9_conn_cancel+0xaa/0x970 net/9p/trans_fd.c:192

stack backtrace:
CPU: 1 PID: 1590 Comm: kworker/1:2 Not tainted 5.19.0-next-20220808-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
Workqueue: events p9_poll_workfn
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2988 [inline]
 check_deadlock kernel/locking/lockdep.c:3031 [inline]
 validate_chain kernel/locking/lockdep.c:3816 [inline]
 __lock_acquire.cold+0x116/0x3a7 kernel/locking/lockdep.c:5053
 lock_acquire kernel/locking/lockdep.c:5666 [inline]
 lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:162
 p9_tag_remove net/9p/client.c:367 [inline]
 p9_req_put net/9p/client.c:375 [inline]
 p9_req_put+0xc6/0x250 net/9p/client.c:372
 p9_conn_cancel+0x640/0x970 net/9p/trans_fd.c:213
 p9_poll_mux net/9p/trans_fd.c:627 [inline]
 p9_poll_workfn+0x25d/0x4e0 net/9p/trans_fd.c:1147
 process_one_work+0x991/0x1610 kernel/workqueue.c:2289
 worker_thread+0x665/0x1080 kernel/workqueue.c:2436
 kthread+0x2e4/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
 </TASK>