Patch "nvme: avoid race in shutdown namespace removal" has been added to the 5.14-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    nvme: avoid race in shutdown namespace removal

to the 5.14-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:
     nvme-avoid-race-in-shutdown-namespace-removal.patch
and it can be found in the queue-5.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3d6a9d9500111c2b2ea36e13904daa8652669b2e
Author: Daniel Wagner <dwagner@xxxxxxx>
Date:   Thu Sep 2 11:20:02 2021 +0200

    nvme: avoid race in shutdown namespace removal
    
    [ Upstream commit 9edceaf43050f5ba1dd7d0011bcf68a736a17743 ]
    
    When we remove the siblings entry, we update ns->head->list, hence we
    can't separate the removal and test for being empty. They have to be
    in the same critical section to avoid a race.
    
    To avoid breaking the refcounting imbalance again, add a list empty
    check to nvme_find_ns_head.
    
    Fixes: 5396fdac56d8 ("nvme: fix refcounting imbalance when all paths are down")
    Signed-off-by: Daniel Wagner <dwagner@xxxxxxx>
    Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
    Tested-by: Hannes Reinecke <hare@xxxxxxx>
    Signed-off-by: Christoph Hellwig <hch@xxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 2f0cbaba12ac..84e7cb9f1968 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3496,7 +3496,9 @@ static struct nvme_ns_head *nvme_find_ns_head(struct nvme_subsystem *subsys,
 	lockdep_assert_held(&subsys->lock);
 
 	list_for_each_entry(h, &subsys->nsheads, entry) {
-		if (h->ns_id == nsid && nvme_tryget_ns_head(h))
+		if (h->ns_id != nsid)
+			continue;
+		if (!list_empty(&h->list) && nvme_tryget_ns_head(h))
 			return h;
 	}
 
@@ -3821,6 +3823,10 @@ static void nvme_ns_remove(struct nvme_ns *ns)
 
 	mutex_lock(&ns->ctrl->subsys->lock);
 	list_del_rcu(&ns->siblings);
+	if (list_empty(&ns->head->list)) {
+		list_del_init(&ns->head->entry);
+		last_path = true;
+	}
 	mutex_unlock(&ns->ctrl->subsys->lock);
 
 	synchronize_rcu(); /* guarantee not available in head->list */
@@ -3840,13 +3846,6 @@ static void nvme_ns_remove(struct nvme_ns *ns)
 	list_del_init(&ns->list);
 	up_write(&ns->ctrl->namespaces_rwsem);
 
-	/* Synchronize with nvme_init_ns_head() */
-	mutex_lock(&ns->head->subsys->lock);
-	if (list_empty(&ns->head->list)) {
-		list_del_init(&ns->head->entry);
-		last_path = true;
-	}
-	mutex_unlock(&ns->head->subsys->lock);
 	if (last_path)
 		nvme_mpath_shutdown_disk(ns->head);
 	nvme_put_ns(ns);