[3.16.y-ckt stable] Patch "ext4: fix ZERO_RANGE bug hidden by flag aliasing" has been added to staging queue

[Luis Henriques]

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

    ext4: fix ZERO_RANGE bug hidden by flag aliasing

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 2c18b7a222a2f494c0bd823b674fef808b920333 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso at mit.edu>
Date: Mon, 1 Sep 2014 14:32:09 -0400
Subject: ext4: fix ZERO_RANGE bug hidden by flag aliasing

commit 713e8dde3e71e92db2d8cc8459d236ce1fb576ce upstream.

We accidently aliased EXT4_EX_NOCACHE and EXT4_GET_CONVERT_UNWRITTEN
falgs, which apparently was hiding a bug that was unmasked when this
flag aliasing issue was addressed (see the subsequent commit).  The
reproduction case was:

   fsx -N 10000 -l 500000 -r 4096 -t 4096 -w 4096 -Z -R -W /vdb/junk

... which would cause fsx to report corruption in the data file.

The fix we have is a bit of an overkill, but I'd much rather be
conservative for now, and we can optimize ZERO_RANGE_FL handling
later.  The fact that we need to zap the extent_status cache for the
inode is unfortunate, but correctness is far more important than
performance.

Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Cc: Namjae Jeon <namjae.jeon at samsung.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/ext4/extents.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 467661264ad0..2a4b4f3b1ae2 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4796,7 +4796,8 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 		max_blocks -= lblk;

 	flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT |
-		EXT4_GET_BLOCKS_CONVERT_UNWRITTEN;
+		EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
+		EXT4_EX_NOCACHE;
 	if (mode & FALLOC_FL_KEEP_SIZE)
 		flags |= EXT4_GET_BLOCKS_KEEP_SIZE;

@@ -4834,15 +4835,21 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 		ext4_inode_block_unlocked_dio(inode);
 		inode_dio_wait(inode);

+		ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
+					     flags, mode);
+		if (ret)
+			goto out_dio;
 		/*
 		 * Remove entire range from the extent status tree.
+		 *
+		 * ext4_es_remove_extent(inode, lblk, max_blocks) is
+		 * NOT sufficient.  I'm not sure why this is the case,
+		 * but let's be conservative and remove the extent
+		 * status tree for the entire inode.  There should be
+		 * no outstanding delalloc extents thanks to the
+		 * filemap_write_and_wait_range() call above.
 		 */
-		ret = ext4_es_remove_extent(inode, lblk, max_blocks);
-		if (ret)
-			goto out_dio;
-
-		ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
-					     flags, mode);
+		ret = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
 		if (ret)
 			goto out_dio;
 	}