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Date:   Tue, 13 Feb 2018 19:55:20 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Trond Myklebust <trondmy@...marydata.com>
Cc:     "bot+d8fe95298ef830cd7d05e33eefa4a5a6f6f334d4@...kaller.appspotmail.com" 
        <bot+d8fe95298ef830cd7d05e33eefa4a5a6f6f334d4@...kaller.appspotmail.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bfields@...ldses.org" <bfields@...ldses.org>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "jlayton@...chiereds.net" <jlayton@...chiereds.net>,
        "jiangshanlai@...il.com" <jiangshanlai@...il.com>,
        "anna.schumaker@...app.com" <anna.schumaker@...app.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>,
        "tj@...nel.org" <tj@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: possible deadlock in flush_work (2)

On Mon, Nov 6, 2017 at 11:34 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Sun, Nov 5, 2017 at 5:00 PM, Trond Myklebust <trondmy@...marydata.com> wrote:
>>
>>
>> On Sun, 2017-11-05 at 11:53 +0300, Dmitry Vyukov wrote:
>>> On Sun, Nov 5, 2017 at 11:41 AM, syzbot
>>> <bot+d8fe95298ef830cd7d05e33eefa4a5a6f6f334d4@...kaller.appspotmail.c
>>> om>
>>> wrote:
>>> > Hello,
>>> >
>>> > syzkaller hit the following crash on
>>> > 0f611fb6dcc0d6d91b4e1fec911321f434a3b858
>>> > git://git.cmpxchg.org/linux-mmots.git/master
>>> > compiler: gcc (GCC) 7.1.1 20170620
>>> > .config is attached
>>> > Raw console output is attached.
>>> >
>>> > xs_tcp_setup_socket: connect returned unhandled error -113
>>> > xs_tcp_setup_socket: connect returned unhandled error -113
>>> > xs_tcp_setup_socket: connect returned unhandled error -113
>>> >
>>> > ======================================================
>>> > WARNING: possible circular locking dependency detected
>>> > 4.14.0-rc5-mm1+ #20 Not tainted
>>> > ------------------------------------------------------
>>> > kworker/0:3/3400 is trying to acquire lock:
>>> >  ("xprtiod"){+.+.}, at: [<ffffffff8146adda>] start_flush_work
>>> > kernel/workqueue.c:2850 [inline]
>>> >  ("xprtiod"){+.+.}, at: [<ffffffff8146adda>] flush_work+0x55a/0x8a0
>>> > kernel/workqueue.c:2882
>>> >
>>> > but task is already holding lock:
>>> >  ((&task->u.tk_work)){+.+.}, at: [<ffffffff81471eb2>]
>>> > process_one_work+0xb32/0x1bc0 kernel/workqueue.c:2087
>>> >
>>> > which lock already depends on the new lock.
>>> >
>>> >
>>> > the existing dependency chain (in reverse order) is:
>>> >
>>> > -> #1 ((&task->u.tk_work)){+.+.}:
>>> >        process_one_work+0xba2/0x1bc0 kernel/workqueue.c:2088
>>> >        worker_thread+0x223/0x1990 kernel/workqueue.c:2246
>>> >        kthread+0x38b/0x470 kernel/kthread.c:242
>>> >        ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>>> >
>>> > -> #0 ("xprtiod"){+.+.}:
>>> >        lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3991
>>> >        start_flush_work kernel/workqueue.c:2851 [inline]
>>> >        flush_work+0x57f/0x8a0 kernel/workqueue.c:2882
>>> >        __cancel_work_timer+0x30a/0x7e0 kernel/workqueue.c:2954
>>> >        cancel_work_sync+0x17/0x20 kernel/workqueue.c:2990
>>> >        xprt_destroy+0xa1/0x130 net/sunrpc/xprt.c:1467
>>> >        xprt_destroy_kref net/sunrpc/xprt.c:1477 [inline]
>>> >        kref_put include/linux/kref.h:70 [inline]
>>> >        xprt_put+0x38/0x40 net/sunrpc/xprt.c:1501
>>> >        rpc_task_release_client+0x299/0x430 net/sunrpc/clnt.c:986
>>> >        rpc_release_resources_task+0x7f/0xa0 net/sunrpc/sched.c:1020
>>> >        rpc_release_task net/sunrpc/sched.c:1059 [inline]
>>> >        __rpc_execute+0x4d9/0xe70 net/sunrpc/sched.c:824
>>> >        rpc_async_schedule+0x16/0x20 net/sunrpc/sched.c:848
>>> >        process_one_work+0xbf0/0x1bc0 kernel/workqueue.c:2112
>>> >        worker_thread+0x223/0x1990 kernel/workqueue.c:2246
>>> >        kthread+0x38b/0x470 kernel/kthread.c:242
>>> >        ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>>> >
>>> > other info that might help us debug this:
>>> >
>>> >  Possible unsafe locking scenario:
>>> >
>>> >        CPU0                    CPU1
>>> >        ----                    ----
>>> >   lock((&task->u.tk_work));
>>> >                                lock("xprtiod");
>>> >                                lock((&task->u.tk_work));
>>> >   lock("xprtiod");
>>> >
>>> >  *** DEADLOCK ***
>>> >
>>> > 2 locks held by kworker/0:3/3400:
>>> >  #0:  ("rpciod"){+.+.}, at: [<ffffffff81471e5f>] __write_once_size
>>> > include/linux/compiler.h:305 [inline]
>>> >  #0:  ("rpciod"){+.+.}, at: [<ffffffff81471e5f>] atomic64_set
>>> > arch/x86/include/asm/atomic64_64.h:33 [inline]
>>> >  #0:  ("rpciod"){+.+.}, at: [<ffffffff81471e5f>] atomic_long_set
>>> > include/asm-generic/atomic-long.h:56 [inline]
>>> >  #0:  ("rpciod"){+.+.}, at: [<ffffffff81471e5f>] set_work_data
>>> > kernel/workqueue.c:618 [inline]
>>> >  #0:  ("rpciod"){+.+.}, at: [<ffffffff81471e5f>]
>>> > set_work_pool_and_clear_pending kernel/workqueue.c:645 [inline]
>>> >  #0:  ("rpciod"){+.+.}, at: [<ffffffff81471e5f>]
>>> > process_one_work+0xadf/0x1bc0 kernel/workqueue.c:2083
>>> >  #1:  ((&task->u.tk_work)){+.+.}, at: [<ffffffff81471eb2>]
>>> > process_one_work+0xb32/0x1bc0 kernel/workqueue.c:2087
>>> >
>>> > stack backtrace:
>>> > CPU: 0 PID: 3400 Comm: kworker/0:3 Not tainted 4.14.0-rc5-mm1+ #20
>>> > Hardware name: Google Google Compute Engine/Google Compute Engine,
>>> > BIOS
>>> > Google 01/01/2011
>>> > Workqueue: rpciod rpc_async_schedule
>>> > Call Trace:
>>> >  __dump_stack lib/dump_stack.c:16 [inline]
>>> >  dump_stack+0x194/0x257 lib/dump_stack.c:52
>>> >  print_circular_bug.isra.41+0x342/0x36a
>>> > kernel/locking/lockdep.c:1258
>>> >  check_prev_add kernel/locking/lockdep.c:1901 [inline]
>>> >  check_prevs_add kernel/locking/lockdep.c:2018 [inline]
>>> >  validate_chain kernel/locking/lockdep.c:2460 [inline]
>>> >  __lock_acquire+0x2f55/0x3d50 kernel/locking/lockdep.c:3487
>>> >  lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3991
>>> >  start_flush_work kernel/workqueue.c:2851 [inline]
>>> >  flush_work+0x57f/0x8a0 kernel/workqueue.c:2882
>>> >  __cancel_work_timer+0x30a/0x7e0 kernel/workqueue.c:2954
>>> >  cancel_work_sync+0x17/0x20 kernel/workqueue.c:2990
>>> >  xprt_destroy+0xa1/0x130 net/sunrpc/xprt.c:1467
>>> >  xprt_destroy_kref net/sunrpc/xprt.c:1477 [inline]
>>> >  kref_put include/linux/kref.h:70 [inline]
>>> >  xprt_put+0x38/0x40 net/sunrpc/xprt.c:1501
>>> >  rpc_task_release_client+0x299/0x430 net/sunrpc/clnt.c:986
>>> >  rpc_release_resources_task+0x7f/0xa0 net/sunrpc/sched.c:1020
>>> >  rpc_release_task net/sunrpc/sched.c:1059 [inline]
>>> >  __rpc_execute+0x4d9/0xe70 net/sunrpc/sched.c:824
>>> >  rpc_async_schedule+0x16/0x20 net/sunrpc/sched.c:848
>>> >  process_one_work+0xbf0/0x1bc0 kernel/workqueue.c:2112
>>> >  worker_thread+0x223/0x1990 kernel/workqueue.c:2246
>>> >  kthread+0x38b/0x470 kernel/kthread.c:242
>>> >  ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>>>
>>>
>>> +sunrpc maintainers
>>
>> A fix for this has already been merged. Please retest with an up to
>> date kernel.
>
> Hi,
>
> What's the fix? Please specify it in the following form:
>
>> syzbot will keep track of this bug report.
>> Once a fix for this bug is committed, please reply to this email with:
>> #syz fix: exact-commit-title
>> Note: all commands must start from beginning of the line.
>
> The bot tests HEAD of multiple branches and it needs to know what
> fixes what, because this still happens on other branches. Once the bot
> knows the fix, it will track when the fix reaches all tested branches.

Seems to be this one:

#syz fix: SUNRPC: Destroy transport from the system workqueue

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