[3.16.y-ckt stable] Patch "Btrfs: fix inode eviction infinite loop after extent_same ioctl" 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: fix inode eviction infinite loop after extent_same ioctl

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-ckt11.

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 ac52f6f547fdc437de6ab70db487376ecc45639e Mon Sep 17 00:00:00 2001
From: Filipe Manana <fdmanana at suse.com>
Date: Mon, 30 Mar 2015 18:26:47 +0100
Subject: Btrfs: fix inode eviction infinite loop after extent_same ioctl

commit 113e8283869b9855c8b999796aadd506bbac155f upstream.

If we pass a length of 0 to the extent_same ioctl, we end up locking an
extent range with a start offset greater then its end offset (if the
destination file's offset is greater than zero). This results in a warning
from extent_io.c:insert_state through the following call chain:

  btrfs_extent_same()
    btrfs_double_lock()
      lock_extent_range()
        lock_extent(inode->io_tree, offset, offset + len - 1)
          lock_extent_bits()
            __set_extent_bit()
              insert_state()
                --> WARN_ON(end < start)

This leads to an infinite loop when evicting the inode. This is the same
problem that my previous patch titled
"Btrfs: fix inode eviction infinite loop after cloning into it" addressed
but for the extent_same ioctl instead of the clone ioctl.

Signed-off-by: Filipe Manana <fdmanana at suse.com>
Reviewed-by: Omar Sandoval <osandov at osandov.com>
Signed-off-by: Chris Mason <clm at fb.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/btrfs/ioctl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 4e395f3f251d..c5b7213f267a 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2941,6 +2941,9 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 len,
 	if (src == dst)
 		return -EINVAL;

+	if (len == 0)
+		return 0;
+
 	btrfs_double_lock(src, loff, dst, dst_loff, len);

 	ret = extent_same_check_offsets(src, loff, len);