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thread-pool: avoid deadlock in nested aio_poll() calls

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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 <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2014-07-15 16:44:26 +02:00 committed by Kevin Wolf
parent c2e50e3d11
commit 3c80ca158c
1 changed files with 6 additions and 0 deletions
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6
thread-pool.c
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@ -185,6 +185,12 @@ restart:
QLIST_REMOVE(elem, all);
/* Read state before ret. */
smp_rmb();
/* Schedule ourselves in case elem->common.cb() calls aio_poll() to
* wait for another request that completed at the same time.
*/
qemu_bh_schedule(pool->completion_bh);
elem->common.cb(elem->common.opaque, elem->ret);
qemu_aio_release(elem);
goto restart;