From: Anton Eidelman <anton@lightbitslabs.com>
Date: Mon, 12 Aug 2019 23:00:36 +0300
Subject: nvme-multipath: fix possible I/O hang when paths are updated
Patch-mainline: v5.3-rc6
Git-commit: 504db087aaccdb32af61539916409f7dca31ceb5
References: bsc#1158983

nvme_state_set_live() making a path available triggers requeue_work
in order to resubmit requests that ended up on requeue_list when no
paths were available.

This requeue_work may race with concurrent nvme_ns_head_make_request()
that do not observe the live path yet.
Such concurrent requests may by made by either:
- New IO submission.
- Requeue_work triggered by nvme_failover_req() or another ana_work.

A race may cause requeue_work capture the state of requeue_list before
more requests get onto the list. These requests will stay on the list
forever unless requeue_work is triggered again.

In order to prevent such race, nvme_state_set_live() should
synchronize_srcu(&head->srcu) before triggering the requeue_work and
prevent nvme_ns_head_make_request referencing an old snapshot of the
path list.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anton Eidelman <anton@lightbitslabs.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 drivers/nvme/host/multipath.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -303,6 +303,7 @@ static void nvme_mpath_set_live(struct n
 		srcu_read_unlock(&head->srcu, srcu_idx);
 	}
 
+	synchronize_srcu(&ns->head->srcu);
 	kblockd_schedule_work(&ns->head->requeue_work);
 }