diff mbox series

[08/10] xfs: fix broken variable-sized allocation detection in xfs_rtallocate_extent_block

Message ID 172530106389.3325667.16691450577382253644.stgit@frogsfrogsfrogs (mailing list archive)
State Accepted, archived
Headers show
Series [01/10] xfs: use the recalculated transaction reservation in xfs_growfs_rt_bmblock | expand

Commit Message

Darrick J. Wong Sept. 2, 2024, 6:29 p.m. UTC 
From: Darrick J. Wong <djwong@kernel.org>

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: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_rtalloc.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)
diff mbox series

Patch

diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index d27bfec08ef8..72123e2337d8 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -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;
 
 	/*