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Subject[PATCH 6/12] ext2 balloc: fix _with_rsv freeze
From
Date

Sync up a reservation fix from ext2 in ext3
------------------------------------------------------
Subject: ext2 balloc: fix _with_rsv freeze
From: Hugh Dickins <hugh@veritas.com>

After several days of testing ext2 with reservations, it got caught inside
ext2_try_to_allocate_with_rsv: alloc_new_reservation repeatedly succeeding on
the window [12cff,12d0e], ext2_try_to_allocate repeatedly failing to find the
free block guaranteed to be included (unless there's contention).

Fix the range to find_next_usable_block's memscan: the scan from "here"
(0xcfe) up to (but excluding) "maxblocks" (0xd0e) needs to scan 3 bytes not 2
(the relevant bytes of bitmap in this case being f7 df ff - none 00, but the
premature cutoff implying that the last was found 00).

Is this a problem for mainline ext2? No, because the "size" in its memscan is
always EXT2_BLOCKS_PER_GROUP(sb), which mkfs.ext2 requires to be a multiple of
8. Is this a problem for ext3 or ext4? No, because they have an additional
extN_test_allocatable test which rescues them from the error.

--------------------------------------------------

Signed-off-by: Mingming Cao <cmm@us.ibm.com>


---

linux-2.6.19-rc5-cmm/fs/ext3/balloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN fs/ext3/balloc.c~ext3-balloc-fix-_with_rsv-freeze fs/ext3/balloc.c
--- linux-2.6.19-rc5/fs/ext3/balloc.c~ext3-balloc-fix-_with_rsv-freeze 2006-11-28 19:36:55.000000000 -0800
+++ linux-2.6.19-rc5-cmm/fs/ext3/balloc.c 2006-11-28 19:36:55.000000000 -0800
@@ -730,7 +730,7 @@ find_next_usable_block(ext3_grpblk_t sta
here = 0;

p = ((char *)bh->b_data) + (here >> 3);
- r = memscan(p, 0, (maxblocks - here + 7) >> 3);
+ r = memscan(p, 0, ((maxblocks + 7) >> 3) - (here >> 3));
next = (r - ((char *)bh->b_data)) << 3;

if (next < maxblocks && next >= start && ext3_test_allocatable(next, bh))
_


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