------------------------------------------------------ Subject: ext2 balloc: fix _with_rsv freeze From: Hugh Dickins <hugh@xxxxxxxxxxx> 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. -------------------------------------------------- Sync up a reservation fix from ext2 in ext4 Signed-off-by: Mingming Cao <cmm@xxxxxxxxxx> --- linux-2.6.19-rc5-cmm/fs/ext4/balloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN fs/ext4/balloc.c~ext4-balloc-fix-_with_rsv-freeze fs/ext4/balloc.c --- linux-2.6.19-rc5/fs/ext4/balloc.c~ext4-balloc-fix-_with_rsv-freeze 2006-11-28 19:37:12.000000000 -0800 +++ linux-2.6.19-rc5-cmm/fs/ext4/balloc.c 2006-11-28 19:37:12.000000000 -0800 @@ -747,7 +747,7 @@ find_next_usable_block(ext4_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 && ext4_test_allocatable(next, bh)) _ - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
