aio-wait: avoid AioContext lock in aio_wait_bh_oneshot()
There is no need for the AioContext lock in aio_wait_bh_oneshot().
It's easy to remove the lock from existing callers and then switch from
AIO_WAIT_WHILE() to AIO_WAIT_WHILE_UNLOCKED() in aio_wait_bh_oneshot().
Document that the AioContext lock should not be held across
aio_wait_bh_oneshot(). Holding a lock across aio_poll() can cause
deadlock so we don't want callers to do that.
This is a step towards getting rid of the AioContext lock.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230404153307.458883-1-stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index a620299..af1c24c 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -315,9 +315,10 @@
s->stopping = true;
trace_virtio_blk_data_plane_stop(s);
- aio_context_acquire(s->ctx);
aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
+ aio_context_acquire(s->ctx);
+
/* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */
blk_drain(s->conf->conf.blk);
diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index 20bb917..f3214e1 100644
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -197,9 +197,7 @@
}
s->dataplane_stopping = true;
- aio_context_acquire(s->ctx);
aio_wait_bh_oneshot(s->ctx, virtio_scsi_dataplane_stop_bh, s);
- aio_context_release(s->ctx);
blk_drain_all(); /* ensure there are no in-flight requests */
diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
index 6e43e3b..5449b6d 100644
--- a/include/block/aio-wait.h
+++ b/include/block/aio-wait.h
@@ -131,7 +131,7 @@
*
* Run a BH in @ctx and wait for it to complete.
*
- * Must be called from the main loop thread with @ctx acquired exactly once.
+ * Must be called from the main loop thread without @ctx acquired.
* Note that main loop event processing may occur.
*/
void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque);
diff --git a/util/aio-wait.c b/util/aio-wait.c
index 98c5acc..b5336cf 100644
--- a/util/aio-wait.c
+++ b/util/aio-wait.c
@@ -82,5 +82,5 @@
assert(qemu_get_current_aio_context() == qemu_get_aio_context());
aio_bh_schedule_oneshot(ctx, aio_wait_bh, &data);
- AIO_WAIT_WHILE(ctx, !data.done);
+ AIO_WAIT_WHILE_UNLOCKED(NULL, !data.done);
}
