[PATCH 6.12.y] nvme: add missing SRCU grace period in error path

[Sasha Levin <sashal@kernel.org>]

From: Tristan Madani <tristan@talencesecurity.com>

[ Upstream commit ef248d5de4469fb6bbaf8dbe0c4c47800080d648 ]

nvme_alloc_ns() error path at out_unlink_ns removes ns from the
namespace head siblings list with list_del_rcu(&ns->siblings) but
does not wait for SRCU readers before freeing the namespace struct.
Multipath code iterates the head->list under srcu_read_lock() in
nvme_find_path() and nvme_mpath_revalidate_paths(), so a concurrent
reader can still hold a reference to ns when kfree(ns) runs.

The normal removal path in nvme_ns_remove() correctly calls
synchronize_srcu(&ns->head->srcu) after list_del_rcu() to wait for
in-progress readers. Add the same grace period in the error path.

Fixes: ed754e5deeb1 ("nvme: track shared namespaces")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
[ Adjusted patch context to account for missing last_path reference-counting code. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/nvme/host/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 4b13427d0a8a4..cb36fe02c6457 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3966,6 +3966,9 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info)
 	if (list_empty(&ns->head->list))
 		list_del_init(&ns->head->entry);
 	mutex_unlock(&ctrl->subsys->lock);
+
+	/* guarantee not available in head->list */
+	synchronize_srcu(&ns->head->srcu);
 	nvme_put_ns_head(ns->head);
  out_cleanup_disk:
 	put_disk(disk);
-- 
2.53.0