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Date: Tue, 2 Jan 2007 14:39:09 +0530
From: "Amit K. Arora" <aarora@...ux.vnet.ibm.com>
To: linux-ext4@...r.kernel.org
Cc: suparna@...ibm.com, cmm@...ibm.com, alex@...sterfs.com
Subject: [PATCH 1/1] Extent overlap bugfix in ext4
The ext4_ext_get_blocks() and ext4_ext_insert_extent() routines do not
check for extent overlap, when a new extent needs to be inserted in an
inode. An overlap is possible when the new extent being inserted has
ee_block that is not part of any of the existing extents, but the
tail/center portion of this new extent _is_. This is possible only when
we are writing/preallocating blocks across a hole.
This problem was first sighted while stress testing (using modified
fsx-linux stress test) persistent preallocation patches that I posted
earlier. Though I am not able to reproduce this bug (extent overlap)
without the persistent preallocation patches (because a write through a
hole results in get_blocks() of a single block at a time), but I think
that it is an independant problem and should be solved with a separate
patch. Hence this patch.
Comments please. Thanks!
Signed-off-by: Amit Arora (aarora@...ibm.com)
---
fs/ext4/extents.c | 71 +++++++++++++++++++++++++++++++++++++---
include/linux/ext4_fs_extents.h | 1
2 files changed, 68 insertions(+), 4 deletions(-)
Index: linux-2.6.19.prealloc/fs/ext4/extents.c
===================================================================
--- linux-2.6.19.prealloc.orig/fs/ext4/extents.c 2007-01-02 14:21:57.000000000 +0530
+++ linux-2.6.19.prealloc/fs/ext4/extents.c 2007-01-02 14:22:00.000000000 +0530
@@ -1119,6 +1119,44 @@
}
/*
+ * ext4_ext_check_overlap:
+ * check if a portion of the "newext" extent overlaps with an
+ * existing extent.
+ */
+struct ext4_extent * ext4_ext_check_overlap(struct inode *inode,
+ struct ext4_extent *newext)
+{
+ struct ext4_ext_path *path;
+ struct ext4_extent *ex;
+ unsigned int depth, b1, b2, len1;
+
+ b1 = le32_to_cpu(newext->ee_block);
+ len1 = le16_to_cpu(newext->ee_len);
+ path = ext4_ext_find_extent(inode, b1, NULL);
+ if (IS_ERR(path))
+ return NULL;
+
+ depth = ext_depth(inode);
+ ex = path[depth].p_ext;
+ if (!ex)
+ return NULL;
+
+ b2 = ext4_ext_next_allocated_block(path);
+ if (b2 == EXT_MAX_BLOCK)
+ return NULL;
+ path = ext4_ext_find_extent(inode, b2, path);
+ if (IS_ERR(path))
+ return NULL;
+ BUG_ON(path[depth].p_hdr == NULL);
+ ex = path[depth].p_ext;
+
+ if (b1 + len1 > b2)
+ return ex;
+
+ return NULL;
+}
+
+/*
* ext4_ext_insert_extent:
* tries to merge requsted extent into the existing extent or
* inserts requested extent as new one into the tree,
@@ -1129,7 +1167,7 @@
struct ext4_extent *newext)
{
struct ext4_extent_header * eh;
- struct ext4_extent *ex, *fex;
+ struct ext4_extent *ex, *fex, *rex;
struct ext4_extent *nearex; /* nearest extent */
struct ext4_ext_path *npath = NULL;
int depth, len, err, next;
@@ -1139,6 +1177,18 @@
ex = path[depth].p_ext;
BUG_ON(path[depth].p_hdr == NULL);
+ /* check for overlap */
+ rex = ext4_ext_check_overlap(inode, newext);
+ if (rex) {
+ printk(KERN_ERR "ERROR: ex=%u/%u overlaps newext=%u/%u\n",
+ le32_to_cpu(rex->ee_block),
+ le16_to_cpu(rex->ee_len),
+ le32_to_cpu(newext->ee_block),
+ le16_to_cpu(newext->ee_len));
+ ext4_ext_show_leaf(inode, path);
+ BUG();
+ }
+
/* try to insert block into found extent and return */
if (ex && ext4_can_extents_be_merged(inode, ex, newext)) {
ext_debug("append %d block to %d:%d (from %llu)\n",
@@ -1921,7 +1971,7 @@
int create, int extend_disksize)
{
struct ext4_ext_path *path = NULL;
- struct ext4_extent newex, *ex;
+ struct ext4_extent newex, *ex, *ex2;
ext4_fsblk_t goal, newblock;
int err = 0, depth;
unsigned long allocated = 0;
@@ -1984,6 +2034,10 @@
*/
if (ee_len > EXT_MAX_LEN)
goto out2;
+
+ if (iblock < ee_block && iblock + max_blocks >= ee_block)
+ allocated = ee_block - iblock;
+
/* if found extent covers block, simply return it */
if (iblock >= ee_block && iblock < ee_block + ee_len) {
newblock = iblock - ee_block + ee_start;
@@ -2016,7 +2070,17 @@
/* allocate new block */
goal = ext4_ext_find_goal(inode, path, iblock);
- allocated = max_blocks;
+
+ /* Check if we can really insert (iblock)::(iblock+max_blocks) extent */
+ newex.ee_block = cpu_to_le32(iblock);
+ if (!allocated) {
+ newex.ee_len = cpu_to_le16(max_blocks);
+ ex2 = ext4_ext_check_overlap(inode, &newex);
+ if (ex2)
+ allocated = le32_to_cpu(ex2->ee_block) - iblock;
+ else
+ allocated = max_blocks;
+ }
newblock = ext4_new_blocks(handle, inode, goal, &allocated, &err);
if (!newblock)
goto out2;
@@ -2024,7 +2088,6 @@
goal, newblock, allocated);
/* try to insert new extent into found leaf and return */
- newex.ee_block = cpu_to_le32(iblock);
ext4_ext_store_pblock(&newex, newblock);
newex.ee_len = cpu_to_le16(allocated);
err = ext4_ext_insert_extent(handle, inode, path, &newex);
Index: linux-2.6.19.prealloc/include/linux/ext4_fs_extents.h
===================================================================
--- linux-2.6.19.prealloc.orig/include/linux/ext4_fs_extents.h 2007-01-02 14:21:57.000000000 +0530
+++ linux-2.6.19.prealloc/include/linux/ext4_fs_extents.h 2007-01-02 14:22:00.000000000 +0530
@@ -190,6 +190,7 @@
extern int ext4_extent_tree_init(handle_t *, struct inode *);
extern int ext4_ext_calc_credits_for_insert(struct inode *, struct ext4_ext_path *);
+extern struct ext4_extent * ext4_ext_check_overlap(struct inode *, struct ext4_extent *);
extern int ext4_ext_insert_extent(handle_t *, struct inode *, struct ext4_ext_path *, struct ext4_extent *);
extern int ext4_ext_walk_space(struct inode *, unsigned long, unsigned long, ext_prepare_callback, void *);
extern struct ext4_ext_path * ext4_ext_find_extent(struct inode *, int, struct ext4_ext_path *);
--
Regards,
Amit Arora
-
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