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xfs: fix broken variable-sized allocation detection in xfs_rtallocate_extent_block

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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>
This commit is contained in:
Darrick J. Wong
2024-08-30 15:37:06 -07:00
parent 74c234bbe5
commit 9e9be9840f
1 changed files with 9 additions and 6 deletions
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15
fs/xfs/xfs_rtalloc.c
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@@ -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;
/*