From 69de48445a0d6169f1e2a6c5bfab994e1c810e33 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 3 Oct 2019 11:01:03 +0100 Subject: [PATCH] test-bdrv-drain: fix iothread_join() hang tests/test-bdrv-drain can hang in tests/iothread.c:iothread_run(): while (!atomic_read(&iothread->stopping)) { aio_poll(iothread->ctx, true); } The iothread_join() function works as follows: void iothread_join(IOThread *iothread) { iothread->stopping = true; aio_notify(iothread->ctx); qemu_thread_join(&iothread->thread); If iothread_run() checks iothread->stopping before the iothread_join() thread sets stopping to true, then aio_notify() may be optimized away and iothread_run() hangs forever in aio_poll(). The correct way to change iothread->stopping is from a BH that executes within iothread_run(). This ensures that iothread->stopping is checked after we set it to true. This was already fixed for ./iothread.c (note this is a different source file!) by commit 2362a28ea11c145e1a13ae79342d76dc118a72a6 ("iothread: fix iothread_stop() race condition"), but not for tests/iothread.c. Fixes: 0c330a734b51c177ab8488932ac3b0c4d63a718a ("aio: introduce aio_co_schedule and aio_co_wake") Reported-by: Dr. David Alan Gilbert Reviewed-by: Paolo Bonzini Message-Id: <20191003100103.331-1-stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi --- tests/iothread.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/tests/iothread.c b/tests/iothread.c index 777d9eea46..13c9fdcd8d 100644 --- a/tests/iothread.c +++ b/tests/iothread.c @@ -55,10 +55,16 @@ static void *iothread_run(void *opaque) return NULL; } +static void iothread_stop_bh(void *opaque) +{ + IOThread *iothread = opaque; + + iothread->stopping = true; +} + void iothread_join(IOThread *iothread) { - iothread->stopping = true; - aio_notify(iothread->ctx); + aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread); qemu_thread_join(&iothread->thread); qemu_cond_destroy(&iothread->init_done_cond); qemu_mutex_destroy(&iothread->init_done_lock);