Commit 3c80ca15 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Kevin Wolf
Browse files

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: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent c2e50e3d

thread-pool.c

+6 −0
Original line number Diff line number Diff line
@@ -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;