FAILED: patch "[PATCH] rbd: call rbd_dev_unprobe() after unwatching and flushing" failed to apply to 5.4-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 5.4-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 <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

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

>From 952c48b0ed18919bff7528501e9a3fff8a24f8cd Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <idryomov@xxxxxxxxx>
Date: Mon, 16 Mar 2020 15:52:54 +0100
Subject: [PATCH] rbd: call rbd_dev_unprobe() after unwatching and flushing
 notifies

rbd_dev_unprobe() is supposed to undo most of rbd_dev_image_probe(),
including rbd_dev_header_info(), which means that rbd_dev_header_info()
isn't supposed to be called after rbd_dev_unprobe().

However, rbd_dev_image_release() calls rbd_dev_unprobe() before
rbd_unregister_watch().  This is racy because a header update notify
can sneak in:

  "rbd unmap" thread                   ceph-watch-notify worker

  rbd_dev_image_release()
    rbd_dev_unprobe()
      free and zero out header
                                       rbd_watch_cb()
                                         rbd_dev_refresh()
                                           rbd_dev_header_info()
                                             read in header

The same goes for "rbd map" because rbd_dev_image_probe() calls
rbd_dev_unprobe() on errors.  In both cases this results in a memory
leak.

Fixes: fd22aef8b47c ("rbd: move rbd_unregister_watch() call into rbd_dev_image_release()")
Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Reviewed-by: Jason Dillaman <dillaman@xxxxxxxxxx>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index ff2377e6d12c..7aec8bc5df6e 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -6898,9 +6898,10 @@ static void rbd_print_dne(struct rbd_device *rbd_dev, bool is_snap)
 
 static void rbd_dev_image_release(struct rbd_device *rbd_dev)
 {
-	rbd_dev_unprobe(rbd_dev);
 	if (rbd_dev->opts)
 		rbd_unregister_watch(rbd_dev);
+
+	rbd_dev_unprobe(rbd_dev);
 	rbd_dev->image_format = 0;
 	kfree(rbd_dev->spec->image_id);
 	rbd_dev->spec->image_id = NULL;
@@ -6950,7 +6951,7 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth)
 	if (ret) {
 		if (ret == -ENOENT && !need_watch)
 			rbd_print_dne(rbd_dev, false);
-		goto err_out_watch;
+		goto err_out_probe;
 	}
 
 	/*
@@ -6995,12 +6996,11 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth)
 	return 0;
 
 err_out_probe:
-	rbd_dev_unprobe(rbd_dev);
-err_out_watch:
 	if (!depth)
 		up_write(&rbd_dev->header_rwsem);
 	if (need_watch)
 		rbd_unregister_watch(rbd_dev);
+	rbd_dev_unprobe(rbd_dev);
 err_out_format:
 	rbd_dev->image_format = 0;
 	kfree(rbd_dev->spec->image_id);