Il 15/07/2014 16:44, Stefan Hajnoczi ha scritto:
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 <stefa...@redhat.com> --- thread-pool.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/thread-pool.c b/thread-pool.c index 4cfd078..23888dc 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;
Please make this "return" instead, so that it is clearer that the next invocation of the BH is a continuation of this one.
Paolo
