Commit 9e9be984 authored by Darrick J. Wong's avatar Darrick J. Wong
Browse files

xfs: fix broken variable-sized allocation detection in xfs_rtallocate_extent_block 



This function tries to find a suitable free space extent starting from
a particular rtbitmap block.  Some time ago, I added a clamping function
to prevent the free space scans from running off the end of the bitmap,
but I didn't quite get the logic right.

Let's say there's an allocation request with a minlen of 5 and a maxlen
of 32 and we're scanning the last rtbitmap block.  If we come within 4
rtx of the end of the rt volume, maxlen will get clamped to 4.  If the
next 3 rtx are free, we could have satisfied the allocation, but the
code setting partial besti/bestlen for "minlen < maxlen" will think that
we're doing a non-variable allocation and ignore it.

The root of this problem is overwriting maxlen; I should have stuffed
the results in a different variable, which would not have introduced
this bug.

Signed-off-by: default avatarDarrick J. Wong <djwong@kernel.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
parent 74c234bb

fs/xfs/xfs_rtalloc.c

+9 −6
Original line number Diff line number Diff line
@@ -244,6 +244,7 @@ xfs_rtallocate_extent_block( 
	xfs_rtxnum_t		end;	/* last rtext in chunk */

	xfs_rtxnum_t		i;	/* current rtext trying */

	xfs_rtxnum_t		next;	/* next rtext to try */

	xfs_rtxlen_t		scanlen; /* number of free rtx to look for */

	xfs_rtxlen_t		bestlen = 0; /* best length found so far */

	int			stat;	/* status from internal calls */

	int			error;
@@ -255,20 +256,22 @@ xfs_rtallocate_extent_block( 
	end = min(mp->m_sb.sb_rextents, xfs_rbmblock_to_rtx(mp, bbno + 1)) - 1;

	for (i = xfs_rbmblock_to_rtx(mp, bbno); i <= end; i++) {

		/* Make sure we don't scan off the end of the rt volume. */

		maxlen = xfs_rtallocate_clamp_len(mp, i, maxlen, prod);

		scanlen = xfs_rtallocate_clamp_len(mp, i, maxlen, prod);

		if (scanlen < minlen)

			break;



		/*

		 * See if there's a free extent of maxlen starting at i.

		 * See if there's a free extent of scanlen starting at i.

		 * If it's not so then next will contain the first non-free.

		 */

		error = xfs_rtcheck_range(args, i, maxlen, 1, &next, &stat);

		error = xfs_rtcheck_range(args, i, scanlen, 1, &next, &stat);

		if (error)

			return error;

		if (stat) {

			/*

			 * i for maxlen is all free, allocate and return that.

			 * i to scanlen is all free, allocate and return that.

			 */

			*len = maxlen;

			*len = scanlen;

			*rtx = i;

			return 0;

		}
@@ -299,7 +302,7 @@ xfs_rtallocate_extent_block( 
	}



	/* Searched the whole thing & didn't find a maxlen free extent. */

	if (minlen > maxlen || besti == -1)

	if (besti == -1)

		goto nospace;



	/*