[3.16.y-ckt stable] Patch "Btrfs: send, don't leave without decrementing clone root's send_progress" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    Btrfs: send, don't leave without decrementing clone root's send_progress

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt14.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From e8f6216d4782f57a9a85c59ef53fb033936cc1a8 Mon Sep 17 00:00:00 2001
From: Filipe Manana <fdmanana at suse.com>
Date: Mon, 2 Mar 2015 20:53:53 +0000
Subject: Btrfs: send, don't leave without decrementing clone root's
 send_progress

commit 2f1f465ae6da244099af55c066e5355abd8ff620 upstream.

If the clone root was not readonly or the dead flag was set on it, we were
leaving without decrementing the root's send_progress counter (and before
we just incremented it). If a concurrent snapshot deletion was in progress
and ended up being aborted, it would be impossible to later attempt to
delete again the snapshot, since the root's send_in_progress counter could
never go back to 0.

We were also setting clone_sources_to_rollback to i + 1 too early - if we
bailed out because the clone root we got is not readonly or flagged as dead
we ended up later derreferencing a null pointer because we didn't assign
the clone root to sctx->clone_roots[i].root:

		for (i = 0; sctx && i < clone_sources_to_rollback; i++)
			btrfs_root_dec_send_in_progress(
					sctx->clone_roots[i].root);

So just don't increment the send_in_progress counter if the root is readonly
or flagged as dead.

Signed-off-by: Filipe Manana <fdmanana at suse.com>
Reviewed-by: David Sterba <dsterba at suse.cz>
Signed-off-by: Chris Mason <clm at fb.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/btrfs/send.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 61205f6db114..396ac55ff949 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -5644,9 +5644,7 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
 				ret = PTR_ERR(clone_root);
 				goto out;
 			}
-			clone_sources_to_rollback = i + 1;
 			spin_lock(&clone_root->root_item_lock);
-			clone_root->send_in_progress++;
 			if (!btrfs_root_readonly(clone_root) ||
 			    btrfs_root_dead(clone_root)) {
 				spin_unlock(&clone_root->root_item_lock);
@@ -5654,10 +5652,12 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
 				ret = -EPERM;
 				goto out;
 			}
+			clone_root->send_in_progress++;
 			spin_unlock(&clone_root->root_item_lock);
 			srcu_read_unlock(&fs_info->subvol_srcu, index);

 			sctx->clone_roots[i].root = clone_root;
+			clone_sources_to_rollback = i + 1;
 		}
 		vfree(clone_sources_tmp);
 		clone_sources_tmp = NULL;