From c44245b3d5435f533ca8346ece65918f84c057f9 Mon Sep 17 00:00:00 2001

From: Omar Sandoval <osandov@fb.com>

Date: Fri, 11 Aug 2017 09:00:06 -0700

Subject: [PATCH] xfs: fix inobt inode allocation search optimization

Git-commit: c44245b3d5435f533ca8346ece65918f84c057f9

Patch-mainline: v4.13-rc6

References: bsc#1052766

When we try to allocate a free inode by searching the inobt, we try to

find the inode nearest the parent inode by searching chunks both left

and right of the chunk containing the parent. As an optimization, we

cache the leftmost and rightmost records that we previously searched; if

we do another allocation with the same parent inode, we'll pick up the

search where it last left off.

There's a bug in the case where we found a free inode to the left of the

parent's chunk: we need to update the cached left and right records, but

because we already reassigned the right record to point to the left, we

end up assigning the left record to both the cached left and right

records.

This isn't a correctness problem strictly, but it can result in the next

allocation rechecking chunks unnecessarily or allocating inodes further

away from the parent than it needs to. Fix it by swapping the record

pointer after we update the cached left and right records.

Fixes: bd169565993b ("xfs: speed up free inode search")

Signed-off-by: Omar Sandoval <osandov@fb.com>

Reviewed-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Acked-by: Jan Kara <jack@suse.cz>

---

 fs/xfs/libxfs/xfs_ialloc.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c

index ffd5a15d1bb6..abf5beaae907 100644

--- a/fs/xfs/libxfs/xfs_ialloc.c

+++ b/fs/xfs/libxfs/xfs_ialloc.c

@@ -1246,13 +1246,13 @@ xfs_dialloc_ag_inobt(

 			/* free inodes to the left? */

 			if (useleft && trec.ir_freecount) {

-				rec = trec;

 				xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);

 				cur = tcur;

 				pag->pagl_leftrec = trec.ir_startino;

 				pag->pagl_rightrec = rec.ir_startino;

 				pag->pagl_pagino = pagino;

+				rec = trec;

 				goto alloc_inode;

 			}

-- 

2.12.3