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authorStefan Hajnoczi <stefanha@redhat.com>2014-07-15 16:44:26 +0200
committerKevin Wolf <kwolf@redhat.com>2014-08-15 15:07:14 +0200
commit3c80ca158c96ff902a30883a8933e755988948b1 (patch)
treec1ccc27a2148e1173950d276838803bc5fafcec8 /thread-pool.c
parentc2e50e3d11a0bf4c973cc30478c1af0f2d5f8e81 (diff)
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 <stefanha@redhat.com>
Diffstat (limited to 'thread-pool.c')
-rw-r--r--thread-pool.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/thread-pool.c b/thread-pool.c
index 4cfd07893f..23888dcfc4 100644
--- a/thread-pool.c
+++ b/thread-pool.c
@@ -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;