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[Qemu-devel] [PATCH for-2.11] tests-aio-multithread: fix /aio/multi/sche

From: Stefan Hajnoczi
Subject: [Qemu-devel] [PATCH for-2.11] tests-aio-multithread: fix /aio/multi/schedule race condition
Date: Mon, 6 Nov 2017 19:02:33 +0000

test_multi_co_schedule_entry() set to_schedule[id] in the final loop
iteration before terminating the coroutine.  There is a race condition
where the main thread attempts to enter the terminating or terminated
coroutine when signalling coroutines to stop:

  atomic_mb_set(&now_stopping, true);
  for (i = 0; i < NUM_CONTEXTS; i++) {
      ctx_run(i, finish_cb, NULL);  <--- enters dead coroutine!
      to_schedule[i] = NULL;

Make sure only to set to_schedule[id] if this coroutine really needs to
be scheduled!

Reported-by: "R.Nageswara Sastry" <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
This patch is appropriate for the QEMU 2.11 release to eliminate
spurious test failures.

 tests/test-aio-multithread.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tests/test-aio-multithread.c b/tests/test-aio-multithread.c
index 549d784915..d396185972 100644
--- a/tests/test-aio-multithread.c
+++ b/tests/test-aio-multithread.c
@@ -144,17 +144,16 @@ static void finish_cb(void *opaque)
 static coroutine_fn void test_multi_co_schedule_entry(void *opaque)
     g_assert(to_schedule[id] == NULL);
-    atomic_mb_set(&to_schedule[id], qemu_coroutine_self());
     while (!atomic_mb_read(&now_stopping)) {
         int n;
         n = g_test_rand_int_range(0, NUM_CONTEXTS);
+        atomic_mb_set(&to_schedule[id], qemu_coroutine_self());
         g_assert(to_schedule[id] == NULL);
-        atomic_mb_set(&to_schedule[id], qemu_coroutine_self());

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