@@ -120,17 +120,13 @@ static void scsi_device_for_each_req_async_bh(void *opaque)
SCSIRequest *next;
/*
- * If the AioContext changed before this BH was called then reschedule into
- * the new AioContext before accessing ->requests. This can happen when
- * scsi_device_for_each_req_async() is called and then the AioContext is
- * changed before BHs are run.
+ * The BB cannot have changed contexts between this BH being scheduled and
+ * now: BBs' AioContexts, when they have a node attached, can only be
+ * changed via bdrv_try_change_aio_context(), in a drained section. While
+ * we have the in-flight counter incremented, that drain must block.
*/
ctx = blk_get_aio_context(s->conf.blk);
- if (ctx != qemu_get_current_aio_context()) {
- aio_bh_schedule_oneshot(ctx, scsi_device_for_each_req_async_bh,
- g_steal_pointer(&data));
- return;
- }
+ assert(ctx == qemu_get_current_aio_context());
QTAILQ_FOREACH_SAFE(req, &s->requests, next, next) {
data->fn(req, data->fn_opaque);
@@ -138,11 +134,16 @@ static void scsi_device_for_each_req_async_bh(void *opaque)
/* Drop the reference taken by scsi_device_for_each_req_async() */
object_unref(OBJECT(s));
+
+ /* Paired with blk_inc_in_flight() in scsi_device_for_each_req_async() */
+ blk_dec_in_flight(s->conf.blk);
}
/*
* Schedule @fn() to be invoked for each enqueued request in device @s. @fn()
* runs in the AioContext that is executing the request.
+ * Keeps the BlockBackend's in-flight counter incremented until everything is
+ * done, so draining it will settle all scheduled @fn() calls.
*/
static void scsi_device_for_each_req_async(SCSIDevice *s,
void (*fn)(SCSIRequest *, void *),
@@ -163,6 +164,8 @@ static void scsi_device_for_each_req_async(SCSIDevice *s,
*/
object_ref(OBJECT(s));
+ /* Paired with blk_dec_in_flight() in scsi_device_for_each_req_async_bh() */
+ blk_inc_in_flight(s->conf.blk);
aio_bh_schedule_oneshot(blk_get_aio_context(s->conf.blk),
scsi_device_for_each_req_async_bh,
data);
@@ -1728,11 +1731,20 @@ static void scsi_device_purge_one_req(SCSIRequest *req, void *opaque)
scsi_req_cancel_async(req, NULL);
}
+/**
+ * Cancel all requests, and block until they are deleted.
+ */
void scsi_device_purge_requests(SCSIDevice *sdev, SCSISense sense)
{
scsi_device_for_each_req_async(sdev, scsi_device_purge_one_req, NULL);
+ /*
+ * Await all the scsi_device_purge_one_req() calls scheduled by
+ * scsi_device_for_each_req_async(), and all I/O requests that were
+ * cancelled this way, but may still take a bit of time to settle.
+ */
blk_drain(sdev->conf.blk);
+
scsi_device_set_ua(sdev, sense);
}
scsi_device_for_each_req_async() currently does not provide any way to be awaited. One of its callers is scsi_device_purge_requests(), which therefore currently does not guarantee that all requests are fully settled when it returns. We want all requests to be settled, because scsi_device_purge_requests() is called through the unrealize path, including the one invoked by virtio_scsi_hotunplug() through qdev_simple_device_unplug_cb(), which most likely assumes that all SCSI requests are done then. In fact, scsi_device_purge_requests() already contains a blk_drain(), but this will not fully await scsi_device_for_each_req_async(), only the I/O requests it potentially cancels (not the non-I/O requests). However, we can have scsi_device_for_each_req_async() increment the BB in-flight counter, and have scsi_device_for_each_req_async_bh() decrement it when it is done. This way, the blk_drain() will fully await all SCSI requests to be purged. This also removes the need for scsi_device_for_each_req_async_bh() to double-check the current context and potentially re-schedule itself, should it now differ from the BB's context: Changing a BB's AioContext with a root node is done through bdrv_try_change_aio_context(), which creates a drained section. With this patch, we keep the BB in-flight counter elevated throughout, so we know the BB's context cannot change. Signed-off-by: Hanna Czenczek <hreitz@redhat.com> --- hw/scsi/scsi-bus.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-)