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: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index d27bfec08ef80d0d34f2f5d64615b2a19ef9730e..72123e2337d8518de91b3c2c942e1e2fdb9a062f 100644 (file)
--- 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;
 
        /*