This is a note to let you know that I've just added the patch titled
vhost: Use virtqueue mutex for swapping worker
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
vhost-use-virtqueue-mutex-for-swapping-worker.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 8c96758e5a7097581d2df95f2db42be293f0f52c
Author: Mike Christie <michael.christie@xxxxxxxxxx>
Date: Fri Mar 15 19:47:04 2024 -0500
vhost: Use virtqueue mutex for swapping worker
[ Upstream commit 34cf9ba5f00a222dddd9fc71de7c68fdaac7fb97 ]
__vhost_vq_attach_worker uses the vhost_dev mutex to serialize the
swapping of a virtqueue's worker. This was done for simplicity because
we are already holding that mutex.
In the next patches where the worker can be killed while in use, we need
finer grained locking because some drivers will hold the vhost_dev mutex
while flushing. However in the SIGKILL handler in the next patches, we
will need to be able to swap workers (set current one to NULL), kill
queued works and stop new flushes while flushes are in progress.
To prepare us, this has us use the virtqueue mutex for swapping workers
instead of the vhost_dev one.
Signed-off-by: Mike Christie <michael.christie@xxxxxxxxxx>
Message-Id: <20240316004707.45557-7-michael.christie@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 88362c0afe452..67bd947cc556d 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -664,16 +664,22 @@ static void __vhost_vq_attach_worker(struct vhost_virtqueue *vq,
{
struct vhost_worker *old_worker;
- old_worker = rcu_dereference_check(vq->worker,
- lockdep_is_held(&vq->dev->mutex));
-
mutex_lock(&worker->mutex);
- worker->attachment_cnt++;
- mutex_unlock(&worker->mutex);
+ mutex_lock(&vq->mutex);
+
+ old_worker = rcu_dereference_check(vq->worker,
+ lockdep_is_held(&vq->mutex));
rcu_assign_pointer(vq->worker, worker);
+ worker->attachment_cnt++;
- if (!old_worker)
+ if (!old_worker) {
+ mutex_unlock(&vq->mutex);
+ mutex_unlock(&worker->mutex);
return;
+ }
+ mutex_unlock(&vq->mutex);
+ mutex_unlock(&worker->mutex);
+
/*
* Take the worker mutex to make sure we see the work queued from
* device wide flushes which doesn't use RCU for execution.
