linux-kernel - Re: [PATCH v3] bcache: fix deadlock in bcache

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Date:   Thu, 10 Oct 2019 17:21:24 +0200
From:   Andrea Righi <andrea.righi@...onical.com>
To:     Coly Li <colyli@...e.de>
Cc:     Kent Overstreet <kent.overstreet@...il.com>,
        linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] bcache: fix deadlock in bcache_allocator

On Wed, Aug 07, 2019 at 09:53:46PM +0800, Coly Li wrote:
> On 2019/8/7 6:38 下午, Andrea Righi wrote:
> > bcache_allocator can call the following:
> > 
> >  bch_allocator_thread()
> >   -> bch_prio_write()
> >      -> bch_bucket_alloc()
> >         -> wait on &ca->set->bucket_wait
> > 
> > But the wake up event on bucket_wait is supposed to come from
> > bch_allocator_thread() itself => deadlock:
> > 
> > [ 1158.490744] INFO: task bcache_allocato:15861 blocked for more than 10 seconds.
> > [ 1158.495929]       Not tainted 5.3.0-050300rc3-generic #201908042232
> > [ 1158.500653] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > [ 1158.504413] bcache_allocato D    0 15861      2 0x80004000
> > [ 1158.504419] Call Trace:
> > [ 1158.504429]  __schedule+0x2a8/0x670
> > [ 1158.504432]  schedule+0x2d/0x90
> > [ 1158.504448]  bch_bucket_alloc+0xe5/0x370 [bcache]
> > [ 1158.504453]  ? wait_woken+0x80/0x80
> > [ 1158.504466]  bch_prio_write+0x1dc/0x390 [bcache]
> > [ 1158.504476]  bch_allocator_thread+0x233/0x490 [bcache]
> > [ 1158.504491]  kthread+0x121/0x140
> > [ 1158.504503]  ? invalidate_buckets+0x890/0x890 [bcache]
> > [ 1158.504506]  ? kthread_park+0xb0/0xb0
> > [ 1158.504510]  ret_from_fork+0x35/0x40
> > 
> > Fix by making the call to bch_prio_write() non-blocking, so that
> > bch_allocator_thread() never waits on itself.
> > 
> > Moreover, make sure to wake up the garbage collector thread when
> > bch_prio_write() is failing to allocate buckets.
> > 
> > BugLink: https://bugs.launchpad.net/bugs/1784665
> > BugLink: https://bugs.launchpad.net/bugs/1796292
> > Signed-off-by: Andrea Righi <andrea.righi@...onical.com>
> 
> OK, I add this version into my for-test directory. Once you have a new
> version, I will update it. Thanks.
> 
> Coly Li

Hi Coly,

any news about this patch? We're still using it in Ubuntu and no errors
have been reported so far. Do you think we can add this to linux-next?

Thanks,
-Andrea