[Devel] [PATCH v3 VZ10 1/1] vhost-blk: fix in-flight request counter leakage

[Andrey Drobyshev]

Upon request completion, vhost_blk_handle_host_kick() pops the request from
the queue and writes one status byte into the guest's status iov via
vhost_blk_set_status().

If for whatever reason vhost_blk_set_status() fails (e.g. virtio device
reset/disable on that queue, or QEMU-driven device state changes like
block_resize) - we end up forgetting to call forget_request() and
decrease the in-flight counter.  Thus it remains > 0 forever.

Later upon guest shutdown, when flush happens, we end up forever waiting
in D state in vhost_blk_flush() on this operation:

  wait_event(blk->flush_wait, !atomic_read(&blk->req_inflight[flush_bin]));

So that even SIGKILL can't reap the QEMU process.  That's exactly what
we observed in hci-volumes test after block_resize.

Fix by adjusting the loop body so that forget_request() is always called
unconditionally.

https://virtuozzo.atlassian.net/browse/VSTOR-132571
Fixes: 40a5928ec730 ("drivers/vhost: vhost-blk accelerator for virtio-blk guests")
Signed-off-by: Andrey Drobyshev <andrey.drobyshev at virtuozzo.com>
---
v2 -> v3:
  * Suppress possible return value for vhost_blk_set_status().

v1 -> v2:
  * Don't skip calling vhost_add_used().  Just remove if(...) clause and
    call vhost_blk_set_status(), vhost_add_used() and forget_request()
    unconditionally.

 drivers/vhost/blk.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/vhost/blk.c b/drivers/vhost/blk.c
index f8bedc3e0ee8..996bde9f546c 100644
--- a/drivers/vhost/blk.c
+++ b/drivers/vhost/blk.c
@@ -565,7 +565,6 @@ static void vhost_blk_handle_host_kick(struct vhost_work *work)
 	struct vhost_blk *blk = NULL;
 	bool added;
 	u8 status;
-	int ret;
 
 	blk_vq = container_of(work, struct vhost_blk_vq, work);
 	vq = &blk_vq->vq;
@@ -585,9 +584,7 @@ static void vhost_blk_handle_host_kick(struct vhost_work *work)
 		vhost_blk_req_cleanup(req);
 
 		status = req->bio_err == 0 ?  VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR;
-		ret = vhost_blk_set_status(req, status);
-		if (unlikely(ret))
-			continue;
+		(void) vhost_blk_set_status(req, status);
 
 		vhost_add_used(vq, req->head, req->len);
 		added = true;
-- 
2.47.1