FAILED: patch "[PATCH] nvme: add missing SRCU grace period in error path" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x ef248d5de4469fb6bbaf8dbe0c4c47800080d648
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090941-alumni-snare-26ce@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ef248d5de4469fb6bbaf8dbe0c4c47800080d648 Mon Sep 17 00:00:00 2001
From: Tristan Madani <[email protected]>
Date: Sat, 15 Aug 2026 00:14:27 +0000
Subject: [PATCH] nvme: add missing SRCU grace period in error path

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.

index 5f2744be7388..9739ce38b73a 100644
@@ -4345,6 +4345,9 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info)
 			last_path = true;
 	}
 	mutex_unlock(&ctrl->subsys->lock);
+
+	/* guarantee not available in head->list */
+	synchronize_srcu(&ns->head->srcu);
 	if (last_path)
 		nvme_put_ns_head(ns->head);
 	nvme_put_ns_head(ns->head);

From: Tristan Madani <[email protected]>

[ 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.

---
 drivers/nvme/host/core.c | 3 +++
 1 file changed, 3 insertions(+)

index 0429ddda73be8..783758db4af78 100644
@@ -3953,6 +3953,9 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid,
 	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:
 	blk_cleanup_disk(disk);

2.53.0