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Re: [Qemu-devel] [Qemu-stable] [PATCH] stream: fix the deadlock bug when
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [Qemu-stable] [PATCH] stream: fix the deadlock bug when stream finish |
Date: |
Wed, 27 Aug 2014 18:28:23 +0200 |
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Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 |
Il 27/08/2014 17:53, Michael Roth ha scritto:
>> In case VM does IO while we run a stream job.
>> When stream finishes, the stream coroutine drains all IOs before
>> close the unused image, in bdrv_drain_all() it may find
>> a pending request which is submitted by guest IO coroutine.
>> In order to wait the pending req finish, the subsequent aio_poll()
>> call poll() to wait the req. however, if the req is already done by
>> threadpool and is waiting for the callback, there is no chance to switch
>> back to guest IO coroutine to call the callback and so that the stream
>> coroutine waits in poll() all the time.
This is the same bug fixed by this patch;
commit 3c80ca158c96ff902a30883a8933e755988948b1
Author: Stefan Hajnoczi <address@hidden>
Date: Tue Jul 15 16:44:26 2014 +0200
thread-pool: avoid deadlock in nested aio_poll() calls
The thread pool has a race condition if two elements complete before
thread_pool_completion_bh() runs:
If element A's callback waits for element B using aio_poll() it will
deadlock since pool->completion_bh is not marked scheduled when the
nested aio_poll() runs.
Fix this by marking the BH scheduled while thread_pool_completion_bh()
is executing. This way any nested aio_poll() loops will enter
thread_pool_completion_bh() and complete the remaining elements.
Signed-off-by: Stefan Hajnoczi <address@hidden>
Paolo