Patch "nvme: don't protect ns mutation with ns->head->lock" has been added to the 5.7-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    nvme: don't protect ns mutation with ns->head->lock

to the 5.7-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-don-t-protect-ns-mutation-with-ns-head-lock.patch
and it can be found in the queue-5.7 subdirectory.

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



commit 8d0ffa27e8d59e467282893e4e3151bd363c07a7
Author: Sagi Grimberg <sagi@xxxxxxxxxxx>
Date:   Wed Jun 24 01:53:10 2020 -0700

    nvme: don't protect ns mutation with ns->head->lock
    
    [ Upstream commit e164471dcf19308d154adb69e7760d8ba426a77f ]
    
    Right now ns->head->lock is protecting namespace mutation
    which is wrong and unneeded. Move it to only protect
    against head mutations. While we're at it, remove unnecessary
    ns->head reference as we already have head pointer.
    
    The problem with this is that the head->lock spans
    mpath disk node I/O that may block under some conditions (if
    for example the controller is disconnecting or the path
    became inaccessible), The locking scheme does not allow any
    other path to enable itself, preventing blocked I/O to complete
    and forward-progress from there.
    
    This is a preparation patch for the fix in a subsequent patch
    where the disk I/O will also be done outside the head->lock.
    
    Fixes: 0d0b660f214d ("nvme: add ANA support")
    Signed-off-by: Anton Eidelman <anton@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
    Signed-off-by: Christoph Hellwig <hch@xxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index fece4654fa3e7..f4287d8550a9f 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -410,11 +410,10 @@ static void nvme_mpath_set_live(struct nvme_ns *ns)
 {
 	struct nvme_ns_head *head = ns->head;
 
-	lockdep_assert_held(&ns->head->lock);
-
 	if (!head->disk)
 		return;
 
+	mutex_lock(&head->lock);
 	if (!(head->disk->flags & GENHD_FL_UP))
 		device_add_disk(&head->subsys->dev, head->disk,
 				nvme_ns_id_attr_groups);
@@ -427,9 +426,10 @@ static void nvme_mpath_set_live(struct nvme_ns *ns)
 			__nvme_find_path(head, node);
 		srcu_read_unlock(&head->srcu, srcu_idx);
 	}
+	mutex_unlock(&head->lock);
 
-	synchronize_srcu(&ns->head->srcu);
-	kblockd_schedule_work(&ns->head->requeue_work);
+	synchronize_srcu(&head->srcu);
+	kblockd_schedule_work(&head->requeue_work);
 }
 
 static int nvme_parse_ana_log(struct nvme_ctrl *ctrl, void *data,
@@ -484,14 +484,12 @@ static inline bool nvme_state_is_live(enum nvme_ana_state state)
 static void nvme_update_ns_ana_state(struct nvme_ana_group_desc *desc,
 		struct nvme_ns *ns)
 {
-	mutex_lock(&ns->head->lock);
 	ns->ana_grpid = le32_to_cpu(desc->grpid);
 	ns->ana_state = desc->state;
 	clear_bit(NVME_NS_ANA_PENDING, &ns->flags);
 
 	if (nvme_state_is_live(ns->ana_state))
 		nvme_mpath_set_live(ns);
-	mutex_unlock(&ns->head->lock);
 }
 
 static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
@@ -670,10 +668,8 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
 			nvme_update_ns_ana_state(&desc, ns);
 		}
 	} else {
-		mutex_lock(&ns->head->lock);
 		ns->ana_state = NVME_ANA_OPTIMIZED; 
 		nvme_mpath_set_live(ns);
-		mutex_unlock(&ns->head->lock);
 	}
 
 	if (bdi_cap_stable_pages_required(ns->queue->backing_dev_info)) {