FAILED: patch "[PATCH] ceph: cancel delayed work instead of flushing on mdsc" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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]>.

thanks,

greg k-h

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

From b4002173b7989588b6feaefc42edaf011b596782 Mon Sep 17 00:00:00 2001
From: Jeff Layton <[email protected]>
Date: Tue, 27 Jul 2021 15:47:12 -0400
Subject: [PATCH] ceph: cancel delayed work instead of flushing on mdsc
teardown

The first thing metric_delayed_work does is check mdsc->stopping, and then return immediately if it's set. That's good since we would have already torn down the metric structures at this point, otherwise, but there is no locking around mdsc->stopping.

It's possible that the ceph_metric_destroy call could race with the delayed_work, in which case we could end up with the delayed_work accessing destroyed percpu variables.

At this point in the mdsc teardown, the "stopping" flag has already been set, so there's no benefit to flushing the work. Move the work cancellation in ceph_metric_destroy ahead of the percpu variable destruction, and eliminate the flush_delayed_work call in ceph_mdsc_destroy.

index d98a3eda0d4c..85934091e024 100644
@@ -4954,7 +4954,6 @@ void ceph_mdsc_destroy(struct ceph_fs_client *fsc)
 
 	ceph_metric_destroy(&mdsc->metric);
 
-	flush_delayed_work(&mdsc->metric.delayed_work);
 	fsc->mdsc = NULL;
 	kfree(mdsc);
 	dout("mdsc_destroy %p done\n", mdsc);

index 5ac151eb0d49..04d5df29bbbf 100644
@@ -302,6 +302,8 @@ void ceph_metric_destroy(struct ceph_client_metric *m)
 	if (!m)
 		return;
 
+	cancel_delayed_work_sync(&m->delayed_work);
+
 	percpu_counter_destroy(&m->total_inodes);
 	percpu_counter_destroy(&m->opened_inodes);
 	percpu_counter_destroy(&m->i_caps_mis);

@@ -309,8 +311,6 @@ void ceph_metric_destroy(struct ceph_client_metric *m)
 	percpu_counter_destroy(&m->d_lease_mis);
 	percpu_counter_destroy(&m->d_lease_hit);
 
-	cancel_delayed_work_sync(&m->delayed_work);
-
 	ceph_put_mds_session(m->session);
 }