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SubjectRe: [PATCH v3] bcache: fix deadlock in bcache_allocator
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On 2019/10/10 11:21 下午, Andrea Righi wrote:
> 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@canonical.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

It has been testing on your side for quite long time, and I don't have
better idea on the fix. It looks solid enough, and indeed I have it in
my development patches already with more testing.

> have been reported so far. Do you think we can add this to linux-next?

Yes, this is my plan. It is in my testing queue with other developing
patches.

Thanks.

--

Coly Li

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