From: Christoph Paasch <christoph.paasch@uclouvain.be>
To: Neil Horman <nhorman@tuxdriver.com>
Cc: Bart Van Assche <bvanassche@acm.org>,
David Miller <davem@davemloft.net>,
netdev@vger.kernel.org
Subject: Re: [PATCH RFC] spinlock: split out debugging check from spin_lock_mutex
Date: Thu, 11 Apr 2013 17:54:28 +0200 [thread overview]
Message-ID: <2032636.RnfJ0d1BWA@cpaasch-mac> (raw)
In-Reply-To: <1365693486-6315-1-git-send-email-nhorman@tuxdriver.com>
On Thursday 11 April 2013 11:18:06 Neil Horman wrote:
> Bart, this patch should fix your problem. Could you please test it and
> confirm?
>
> Bart Van Assche recently reported a warning to me:
>
> <IRQ> [<ffffffff8103d79f>] warn_slowpath_common+0x7f/0xc0
> [<ffffffff8103d7fa>] warn_slowpath_null+0x1a/0x20
> [<ffffffff814761dd>] mutex_trylock+0x16d/0x180
> [<ffffffff813968c9>] netpoll_poll_dev+0x49/0xc30
> [<ffffffff8136a2d2>] ? __alloc_skb+0x82/0x2a0
> [<ffffffff81397715>] netpoll_send_skb_on_dev+0x265/0x410
> [<ffffffff81397c5a>] netpoll_send_udp+0x28a/0x3a0
> [<ffffffffa0541843>] ? write_msg+0x53/0x110 [netconsole]
> [<ffffffffa05418bf>] write_msg+0xcf/0x110 [netconsole]
> [<ffffffff8103eba1>] call_console_drivers.constprop.17+0xa1/0x1c0
> [<ffffffff8103fb76>] console_unlock+0x2d6/0x450
> [<ffffffff8104011e>] vprintk_emit+0x1ee/0x510
> [<ffffffff8146f9f6>] printk+0x4d/0x4f
> [<ffffffffa0004f1d>] scsi_print_command+0x7d/0xe0 [scsi_mod]
>
> This resulted from my commit ca99ca14c which introduced a mutex_trylock
> operation in a path that could execute in interrupt context. When mutex
> debugging is enabled, the above warns the user when we are in fact
> exectuting in interrupt context.
>
> I think this is a false positive however. The check is intended to catch
> users who might be issuing sleeping calls in irq context, but the use of
> mutex_trylock here is guaranteed not to sleep.
Even if he does not sleep, may we still hit a deadlock like the following:
netpoll_rx_disable() calls mutex_lock(), who ends up in __mutex_lock_common,
calling spin_lock_mutex().
Immediatly after that, on the same CPU, the interrupt comes and
netpoll_poll_dev calls mutex_trylock and ends up also calling
spin_lock_mutex(). Now, it seems to me that we are deadlocked - the interrupt
is spinning on the lock, because netpoll_rx_disable() already took it.
Or maybe I am missing something?
Cheers,
Christoph
--
IP Networking Lab --- http://inl.info.ucl.ac.be
MultiPath TCP in the Linux Kernel --- http://multipath-tcp.org
UCLouvain
--
next prev parent reply other threads:[~2013-04-11 15:54 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-11 13:42 Netpoll triggers soft lockup Bart Van Assche
2013-04-11 14:08 ` Neil Horman
2013-04-11 15:18 ` [PATCH RFC] spinlock: split out debugging check from spin_lock_mutex Neil Horman
2013-04-11 15:54 ` Christoph Paasch [this message]
2013-04-11 17:04 ` Neil Horman
2013-04-11 17:51 ` Christoph Paasch
2013-04-11 15:57 ` Eric Dumazet
2013-04-11 16:56 ` Neil Horman
2013-04-11 17:31 ` Bart Van Assche
2013-04-11 17:52 ` Neil Horman
2013-04-11 19:14 ` Neil Horman
2013-04-12 6:27 ` Bart Van Assche
2013-04-12 11:32 ` Neil Horman
2013-04-12 14:01 ` Bart Van Assche
2013-04-12 18:45 ` Neil Horman
2013-04-13 7:35 ` Bart Van Assche
2013-04-13 12:03 ` Neil Horman
2013-04-15 14:16 ` Neil Horman
[not found] ` <CAO+b5-oBfH3M0dnrQSs-p1BF_5hKy2tsU-dD=EP9+S=iqPs5ew@mail.gmail.com>
2013-04-16 17:24 ` Neil Horman
2013-04-18 19:29 ` Neil Horman
2013-04-22 20:12 ` Neil Horman
[not found] ` <CAO+b5-r5jVJNZWuREUH5MQ3baeSPR8fVV1p9pMnukmiZd9nRhg@mail.gmail.com>
2013-04-23 13:23 ` Neil Horman
[not found] ` <CAO+b5-rQPyO9QE9v+oQTeo+G-ftcsehSB5=63AZ13QW4EJ1X0Q@mail.gmail.com>
2013-04-23 13:44 ` Neil Horman
2013-04-23 17:33 ` David Miller
2013-04-23 17:50 ` Neil Horman
2013-04-27 18:53 ` bvba Bart Van Assche
2013-04-29 18:13 ` Neil Horman
2013-04-29 19:12 ` Bart Van Assche
2013-04-30 15:35 ` [PATCH RFC] netpoll: convert mutex into a semaphore Neil Horman
2013-05-01 19:00 ` David Miller
2013-05-01 19:34 ` Neil Horman
2013-04-19 8:38 ` [PATCH RFC] spinlock: split out debugging check from spin_lock_mutex Ingo Molnar
2013-04-19 12:52 ` Neil Horman
2013-04-28 2:34 Neil Horman
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