linux-ext4 - [PATCH] ext4: no need to remove extent if len is 0 in ext4_es_remove

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Message-Id: <1361511243-2458-1-git-send-email-guaneryu@gmail.com>
Date:	Fri, 22 Feb 2013 13:34:03 +0800
From:	Eryu Guan <guaneryu@...il.com>
To:	linux-ext4@...r.kernel.org
Cc:	Eryu Guan <guaneryu@...il.com>, Zheng Liu <wenqing.lz@...bao.com>,
	"Theodore Ts'o" <tytso@....edu>
Subject: [PATCH] ext4: no need to remove extent if len is 0 in ext4_es_remove_extent()

len is 0 means no extent needs to be removed, so return immediately.
Otherwise it could trigger the following BUG_ON()

	436	end = offset + len - 1;
	437	BUG_ON(end < offset);

This could be reproduced by a simple truncate(1) command by an
unprivileged user

	truncate -s $(($((2**32 - 1)) * 4096)) /mnt/ext4/testfile

The same is true for __es_insert_extent().

Patched kernel passed xfstests regression test.

Also remove comments about EXT4_I(inode)->i_es_lock, this rwlock
isn't hold by callers.

Cc: Zheng Liu <wenqing.lz@...bao.com>
Cc: "Theodore Ts'o" <tytso@....edu>
Signed-off-by: Eryu Guan <guaneryu@...il.com>
---
 fs/ext4/extents_status.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 564d981..3ac09ca 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -328,6 +328,9 @@ static int __es_insert_extent(struct ext4_es_tree *tree, ext4_lblk_t offset,
 	struct extent_status *es;
 	ext4_lblk_t end = offset + len - 1;
 
+	if (!len)
+		return 0;
+
 	BUG_ON(end < offset);
 	es = tree->cache_es;
 	if (es && offset == (extent_status_end(es) + 1)) {
@@ -386,7 +389,6 @@ out:
 
 /*
  * ext4_es_insert_extent() adds a space to a delayed extent tree.
- * Caller holds inode->i_es_lock.
  *
  * ext4_es_insert_extent is called by ext4_da_write_begin and
  * ext4_es_remove_extent.
@@ -415,7 +417,6 @@ int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t offset,
 
 /*
  * ext4_es_remove_extent() removes a space from a delayed extent tree.
- * Caller holds inode->i_es_lock.
  *
  * Return 0 on success, error code on failure.
  */
@@ -433,6 +434,9 @@ int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t offset,
 	es_debug("remove [%u/%u) from extent status tree of inode %lu\n",
 		 offset, len, inode->i_ino);
 
+	if (!len)
+		return err;
+
 	end = offset + len - 1;
 	BUG_ON(end < offset);
 	write_lock(&EXT4_I(inode)->i_es_lock);
-- 
1.8.1.2

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