From ec00022030da5761518476096626338bd67df57a Mon Sep 17 00:00:00 2001
From: Tahsin Erdogan <tahsin@google.com>
Date: Sat, 5 Aug 2017 22:41:42 -0400
Subject: [PATCH] ext4: inplace xattr block update fails to deduplicate blocks
When an xattr block has a single reference, block is updated inplace
and it is reinserted to the cache. Later, a cache lookup is performed
to see whether an existing block has the same contents. This cache
lookup will most of the time return the just inserted entry so
deduplication is not achieved.
Running the following test script will produce two xattr blocks which
can be observed in "File ACL: " line of debugfs output:
mke2fs -b 1024 -I 128 -F -O extent /dev/sdb 1G
mount /dev/sdb /mnt/sdb
touch /mnt/sdb/{x,y}
setfattr -n user.1 -v aaa /mnt/sdb/x
setfattr -n user.2 -v bbb /mnt/sdb/x
setfattr -n user.1 -v aaa /mnt/sdb/y
setfattr -n user.2 -v bbb /mnt/sdb/y
debugfs -R 'stat x' /dev/sdb | cat
debugfs -R 'stat y' /dev/sdb | cat
This patch defers the reinsertion to the cache so that we can locate
other blocks with the same contents.
Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
---
fs/ext4/xattr.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index de217a094733..4025666c5991 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1816,9 +1816,6 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
ea_bdebug(bs->bh, "modifying in-place");
error = ext4_xattr_set_entry(i, s, handle, inode,
true /* is_block */);
- if (!error)
- ext4_xattr_block_cache_insert(ea_block_cache,
- bs->bh);
ext4_xattr_block_csum_set(inode, bs->bh);
unlock_buffer(bs->bh);
if (error == -EFSCORRUPTED)
@@ -1974,6 +1971,7 @@ inserted:
} else if (bs->bh && s->base == bs->bh->b_data) {
/* We were modifying this block in-place. */
ea_bdebug(bs->bh, "keeping this block");
+ ext4_xattr_block_cache_insert(ea_block_cache, bs->bh);
new_bh = bs->bh;
get_bh(new_bh);
} else {