With the following patch we want to call wake coroutine from thread. And it doesn't work with aio_co_wake: Assume we have no iothreads. Assume we have a coroutine A, which waits in the yield point for external aio_co_wake(), and no progress can be done until it happen. Main thread is in blocking aio_poll() (for example, in blk_read()).
Now, in a separate thread we do aio_co_wake(). It calls aio_co_enter(), which goes through last "else" branch and do aio_context_acquire(ctx). Now we have a deadlock, as aio_poll() will not release the context lock until some progress is done, and progress can't be done until aio_co_wake() wake the coroutine A. And it can't because it wait for aio_context_acquire(). Still, aio_co_schedule() works well in parallel with blocking aio_poll(). So we want use it. Let's add a possibility of rescheduling coroutine in same ctx where it was yield'ed. Fetch co->ctx in same way as it is done in aio_co_wake(). Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> --- include/block/aio.h | 2 +- util/async.c | 8 ++++++++ 2 files changed, 9 insertions(+), 1 deletion(-) diff --git a/include/block/aio.h b/include/block/aio.h index 5f342267d5..744b695525 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -643,7 +643,7 @@ static inline bool aio_node_check(AioContext *ctx, bool is_external) /** * aio_co_schedule: - * @ctx: the aio context + * @ctx: the aio context, if NULL, the current ctx of @co will be used. * @co: the coroutine * * Start a coroutine on a remote AioContext. diff --git a/util/async.c b/util/async.c index 674dbefb7c..750be555c6 100644 --- a/util/async.c +++ b/util/async.c @@ -545,6 +545,14 @@ fail: void aio_co_schedule(AioContext *ctx, Coroutine *co) { + if (!ctx) { + /* + * Read coroutine before co->ctx. Matches smp_wmb in + * qemu_coroutine_enter. + */ + smp_read_barrier_depends(); + ctx = qatomic_read(&co->ctx); + } trace_aio_co_schedule(ctx, co); const char *scheduled = qatomic_cmpxchg(&co->scheduled, NULL, __func__); -- 2.29.2