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" <nasastry@in.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
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);
         schedule_next(n);
+
+        atomic_mb_set(&to_schedule[id], qemu_coroutine_self());
         qemu_coroutine_yield();
-
         g_assert(to_schedule[id] == NULL);
-        atomic_mb_set(&to_schedule[id], qemu_coroutine_self());
     }
 }
 
-- 
2.13.6

On 06/11/2017 20:02, Stefan Hajnoczi wrote:
> 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" <nasastry@in.ibm.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> 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);
>          schedule_next(n);
> +
> +        atomic_mb_set(&to_schedule[id], qemu_coroutine_self());
>          qemu_coroutine_yield();
> -
>          g_assert(to_schedule[id] == NULL);
> -        atomic_mb_set(&to_schedule[id], qemu_coroutine_self());
>      }
>  }
>  
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

Paolo

On Mon, Nov 06, 2017 at 07:02:33PM +0000, Stefan Hajnoczi wrote:
> 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" <nasastry@in.ibm.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> 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(-)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan