linux-kernel - [PATCH 3.16 012/136] ext4: fix interaction between i_size, fallocate, and delalloc after a crash

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Message-ID: <lsq.1518323471.514559988@decadent.org.uk>
Date:   Sun, 11 Feb 2018 04:31:11 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Amir Goldstein" <amir73il@...il.com>,
        "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 3.16 012/136] ext4: fix interaction between i_size,
 fallocate, and delalloc after a crash

3.16.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@....edu>

commit 51e3ae81ec58e95f10a98ef3dd6d7bce5d8e35a2 upstream.

If there are pending writes subject to delayed allocation, then i_size
will show size after the writes have completed, while i_disksize
contains the value of i_size on the disk (since the writes have not
been persisted to disk).

If fallocate(2) is called with the FALLOC_FL_KEEP_SIZE flag, either
with or without the FALLOC_FL_ZERO_RANGE flag set, and the new size
after the fallocate(2) is between i_size and i_disksize, then after a
crash, if a journal commit has resulted in the changes made by the
fallocate() call to be persisted after a crash, but the delayed
allocation write has not resolved itself, i_size would not be updated,
and this would cause the following e2fsck complaint:

Inode 12, end of extent exceeds allowed value
	(logical block 33, physical block 33441, len 7)

This can only take place on a sparse file, where the fallocate(2) call
is allocating blocks in a range which is before a pending delayed
allocation write which is extending i_size.  Since this situation is
quite rare, and the window in which the crash must take place is
typically < 30 seconds, in practice this condition will rarely happen.

Nevertheless, it can be triggered in testing, and in particular by
xfstests generic/456.

Signed-off-by: Theodore Ts'o <tytso@....edu>
Reported-by: Amir Goldstein <amir73il@...il.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/extents.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4810,7 +4810,8 @@ static long ext4_zero_range(struct file
 	}
 
 	if (!(mode & FALLOC_FL_KEEP_SIZE) &&
-	     offset + len > i_size_read(inode)) {
+	    (offset + len > i_size_read(inode) ||
+	     offset + len > EXT4_I(inode)->i_disksize)) {
 		new_size = offset + len;
 		ret = inode_newsize_ok(inode, new_size);
 		if (ret)
@@ -4956,7 +4957,8 @@ long ext4_fallocate(struct file *file, i
 	}
 
 	if (!(mode & FALLOC_FL_KEEP_SIZE) &&
-	     offset + len > i_size_read(inode)) {
+	    (offset + len > i_size_read(inode) ||
+	     offset + len > EXT4_I(inode)->i_disksize)) {
 		new_size = offset + len;
 		ret = inode_newsize_ok(inode, new_size);
 		if (ret)