Date:   Fri, 26 Jul 2019 12:59:40 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+72af434e4b3417318f84@...kaller.appspotmail.com>,
        David Howells <dhowells@...hat.com>,
        David Miller <davem@...emloft.net>,
        linux-afs@...ts.infradead.org, netdev <netdev@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: possible deadlock in rxrpc_put_peer

On Fri, Jul 26, 2019 at 11:38 AM syzbot
<syzbot+72af434e4b3417318f84@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    6d21a41b Add linux-next specific files for 20190718
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=174e3af0600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3430a151e1452331
> dashboard link: https://syzkaller.appspot.com/bug?extid=72af434e4b3417318f84
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>
> 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+72af434e4b3417318f84@...kaller.appspotmail.com

+net/rxrpc/peer_object.c maintainers

> ============================================
> WARNING: possible recursive locking detected
> 5.2.0-next-20190718 #41 Not tainted
> --------------------------------------------
> kworker/0:3/21678 is trying to acquire lock:
> 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at: spin_lock_bh
> /./include/linux/spinlock.h:343 [inline]
> 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
> __rxrpc_put_peer /net/rxrpc/peer_object.c:415 [inline]
> 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
> rxrpc_put_peer+0x2d3/0x6a0 /net/rxrpc/peer_object.c:435
>
> but task is already holding lock:
> 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at: spin_lock_bh
> /./include/linux/spinlock.h:343 [inline]
> 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
> rxrpc_peer_keepalive_dispatch /net/rxrpc/peer_event.c:378 [inline]
> 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
> rxrpc_peer_keepalive_worker+0x6b3/0xd02 /net/rxrpc/peer_event.c:430
>
> other info that might help us debug this:
>   Possible unsafe locking scenario:
>
>         CPU0
>         ----
>    lock(&(&rxnet->peer_hash_lock)->rlock);
>    lock(&(&rxnet->peer_hash_lock)->rlock);
>
>   *** DEADLOCK ***
>
>   May be due to missing lock nesting notation
>
> 3 locks held by kworker/0:3/21678:
>   #0: 000000007c4c2bc3 ((wq_completion)krxrpcd){+.+.}, at: __write_once_size
> /./include/linux/compiler.h:226 [inline]
>   #0: 000000007c4c2bc3 ((wq_completion)krxrpcd){+.+.}, at: arch_atomic64_set
> /./arch/x86/include/asm/atomic64_64.h:34 [inline]
>   #0: 000000007c4c2bc3 ((wq_completion)krxrpcd){+.+.}, at: atomic64_set
> /./include/asm-generic/atomic-instrumented.h:855 [inline]
>   #0: 000000007c4c2bc3 ((wq_completion)krxrpcd){+.+.}, at: atomic_long_set
> /./include/asm-generic/atomic-long.h:40 [inline]
>   #0: 000000007c4c2bc3 ((wq_completion)krxrpcd){+.+.}, at: set_work_data
> /kernel/workqueue.c:620 [inline]
>   #0: 000000007c4c2bc3 ((wq_completion)krxrpcd){+.+.}, at:
> set_work_pool_and_clear_pending /kernel/workqueue.c:647 [inline]
>   #0: 000000007c4c2bc3 ((wq_completion)krxrpcd){+.+.}, at:
> process_one_work+0x88b/0x1740 /kernel/workqueue.c:2240
>   #1: 000000006782bc7f
> ((work_completion)(&rxnet->peer_keepalive_work)){+.+.}, at:
> process_one_work+0x8c1/0x1740 /kernel/workqueue.c:2244
>   #2: 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
> spin_lock_bh /./include/linux/spinlock.h:343 [inline]
>   #2: 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
> rxrpc_peer_keepalive_dispatch /net/rxrpc/peer_event.c:378 [inline]
>   #2: 00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
> rxrpc_peer_keepalive_worker+0x6b3/0xd02 /net/rxrpc/peer_event.c:430
>
> stack backtrace:
> CPU: 0 PID: 21678 Comm: kworker/0:3 Not tainted 5.2.0-next-20190718 #41
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: krxrpcd rxrpc_peer_keepalive_worker
> Call Trace:
>   __dump_stack /lib/dump_stack.c:77 [inline]
>   dump_stack+0x172/0x1f0 /lib/dump_stack.c:113
>   print_deadlock_bug /kernel/locking/lockdep.c:2301 [inline]
>   check_deadlock /kernel/locking/lockdep.c:2342 [inline]
>   validate_chain /kernel/locking/lockdep.c:2881 [inline]
>   __lock_acquire.cold+0x194/0x398 /kernel/locking/lockdep.c:3880
>   lock_acquire+0x190/0x410 /kernel/locking/lockdep.c:4413
>   __raw_spin_lock_bh /./include/linux/spinlock_api_smp.h:135 [inline]
>   _raw_spin_lock_bh+0x33/0x50 /kernel/locking/spinlock.c:175
>   spin_lock_bh /./include/linux/spinlock.h:343 [inline]
>   __rxrpc_put_peer /net/rxrpc/peer_object.c:415 [inline]
>   rxrpc_put_peer+0x2d3/0x6a0 /net/rxrpc/peer_object.c:435
>   rxrpc_peer_keepalive_dispatch /net/rxrpc/peer_event.c:381 [inline]
>   rxrpc_peer_keepalive_worker+0x7a6/0xd02 /net/rxrpc/peer_event.c:430
>   process_one_work+0x9af/0x1740 /kernel/workqueue.c:2269
>   worker_thread+0x98/0xe40 /kernel/workqueue.c:2415
>   kthread+0x361/0x430 /kernel/kthread.c:255
>   ret_from_fork+0x24/0x30 /arch/x86/entry/entry_64.S:352
>
>
> ---
> 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@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
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