[PATCH v2] nvme: Add sibling to list after full initialization

[Daniel Wagner <dwagner@suse.de>]

Adding the newly created namespace before the object is fully
initialized is opening a race with nvme_mpath_revalidate_paths() which
tries to access ns->disk. ns->disk can still be NULL when iterating
over the sibling list.

Signed-off-by: Daniel Wagner <dwagner@suse.de>
---
v2: use list_add_tail_rcu instead of list_add_tail

I got a few bug reports from our customer hitting this
quite often:

 RIP: 0010:nvme_mpath_revalidate_paths+0x27/0xb0 [nvme_core]
 Code: 44 00 00 0f 1f 44 00 00 55 53 48 8b 6f 50 48 8b 55 00 48 8b 85 10 c5 00 00 48 39 d5 48 8b 48 40 74 20 48 8d 42 d0 48 8b 50 20 <48> 3b 4a 40 74 05 f0 80 60 78 ef 48 8b 50 30 48 39 d5 48 8d 42 d0
 RSP: 0018:ffffaf1303fffcc0 EFLAGS: 00010283
 RAX: ffff95f75ef5c400 RBX: ffff95f71f63aa00 RCX: 0000000000200000
 RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff95f71f63aa00
 RBP: ffff95f71b1d0000 R08: 0000000800000000 R09: 00000008ffffffff
 R10: 00000000000007be R11: 0000000000000384 R12: 0000000000000000
 R13: ffff95f71b1d0000 R14: ffff95f721d79338 R15: ffff95f71f63aa00
 FS:  0000000000000000(0000) GS:ffff95f77f9c0000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000040 CR3: 000000033940a005 CR4: 00000000003706e0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  nvme_update_ns_info+0x15b/0x2f0 [nvme_core]
  nvme_alloc_ns+0x27f/0x810 [nvme_core]
  nvme_validate_or_alloc_ns+0xbb/0x190 [nvme_core]
  nvme_scan_work+0x155/0x2d0 [nvme_core]
  process_one_work+0x1f4/0x3e0
  worker_thread+0x24c/0x3e0
  ? process_one_work+0x3e0/0x3e0
  kthread+0x10d/0x130
  ? kthread_park+0xa0/0xa0
  ret_from_fork+0x35/0x40

This patch fixes the problem reported. I am not totally sure why this
suddenly happens but I guess it is related to 041bd1a1fc73 ("nvme:
only call synchronize_srcu when clearing current path").

 drivers/nvme/host/core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 9a2610e147ce..7e43cb31d41e 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3776,7 +3776,6 @@ static int nvme_init_ns_head(struct nvme_ns *ns, unsigned nsid,
 		}
 	}
 
-	list_add_tail_rcu(&ns->siblings, &head->list);
 	ns->head = head;
 	mutex_unlock(&ctrl->subsys->lock);
 	return 0;
@@ -3873,6 +3872,10 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid,
 	if (nvme_update_ns_info(ns, id))
 		goto out_unlink_ns;
 
+	mutex_lock(&ctrl->subsys->lock);
+	list_add_tail_rcu(&ns->siblings, &ns->head->list);
+	mutex_unlock(&ctrl->subsys->lock);
+
 	down_write(&ctrl->namespaces_rwsem);
 	nvme_ns_add_to_ctrl_list(ns);
 	up_write(&ctrl->namespaces_rwsem);
-- 
2.29.2