This is a note to let you know that I've just added the patch titled
ext4: inplace xattr block update fails to deduplicate blocks
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: ext4-inplace-xattr-block-update-fails-to-deduplicate-blocks.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
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: ext4: inplace xattr block update fails to deduplicate blocks
From: Tahsin Erdogan tahsin@google.com
commit ec00022030da5761518476096626338bd67df57a upstream.
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 Signed-off-by: Tommi Rantala tommi.t.rantala@nokia.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/xattr.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -837,8 +837,6 @@ ext4_xattr_block_set(handle_t *handle, s if (!IS_LAST_ENTRY(s->first)) ext4_xattr_rehash(header(s->base), s->here); - ext4_xattr_cache_insert(ext4_mb_cache, - bs->bh); } ext4_xattr_block_csum_set(inode, bs->bh); unlock_buffer(bs->bh); @@ -959,6 +957,7 @@ 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_cache_insert(ext4_mb_cache, bs->bh); new_bh = bs->bh; get_bh(new_bh); } else {
Patches currently in stable-queue which might be from tahsin@google.com are
queue-4.9/ext4-inplace-xattr-block-update-fails-to-deduplicate-blocks.patch