linux-kernel - [PATCH 4.14 038/146] btrfs: tree-check: reduce stack consumption in check_dir

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Message-Id: <20181204103728.388713799@linuxfoundation.org>
Date:   Tue,  4 Dec 2018 11:48:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Josef Bacik <jbacik@...com>,
        Qu Wenruo <wqu@...e.com>, David Sterba <dsterba@...e.com>,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 038/146] btrfs: tree-check: reduce stack consumption in check_dir_item

4.14-stable review patch.  If anyone has any objections, please let me know.

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

commit e2683fc9d219430f5b78889b50cde7f40efeba7b upstream.

I've noticed that the updated item checker stack consumption increased
dramatically in 542f5385e20cf97447 ("btrfs: tree-checker: Add checker
for dir item")

tree-checker.c:check_leaf                    +552 (176 -> 728)

The array is 255 bytes long, dynamic allocation would slow down the
sanity checks so it's more reasonable to keep it on-stack. Moving the
variable to the scope of use reduces the stack usage again

tree-checker.c:check_leaf                    -264 (728 -> 464)

Reviewed-by: Josef Bacik <jbacik@...com>
Reviewed-by: Qu Wenruo <wqu@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Ben Hutchings <ben.hutchings@...ethink.co.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/btrfs/tree-checker.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index 9376739a4cc8..f7e7a455b710 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -212,7 +212,6 @@ static int check_dir_item(struct btrfs_root *root,
 
 	di = btrfs_item_ptr(leaf, slot, struct btrfs_dir_item);
 	while (cur < item_size) {
-		char namebuf[max(BTRFS_NAME_LEN, XATTR_NAME_MAX)];
 		u32 name_len;
 		u32 data_len;
 		u32 max_name_len;
@@ -295,6 +294,8 @@ static int check_dir_item(struct btrfs_root *root,
 		 */
 		if (key->type == BTRFS_DIR_ITEM_KEY ||
 		    key->type == BTRFS_XATTR_ITEM_KEY) {
+			char namebuf[max(BTRFS_NAME_LEN, XATTR_NAME_MAX)];
+
 			read_extent_buffer(leaf, namebuf,
 					(unsigned long)(di + 1), name_len);
 			name_hash = btrfs_name_hash(namebuf, name_len);
-- 
2.17.1