From: Mingming Cao Subject: [PATCH 12/12] ext3 balloc: fix _with_rsv freeze Date: Tue, 28 Nov 2006 20:15:41 -0800 Message-ID: <1164773741.4341.46.camel@localhost.localdomain> References: <20061114014125.dd315fff.akpm@osdl.org> <20061114184919.GA16020@skynet.ie> <20061114113120.d4c22b02.akpm@osdl.org> <20061115214534.72e6f2e8.akpm@osdl.org> <455C0B6F.7000201@us.ibm.com> <20061115232228.afaf42f2.akpm@osdl.org> <1163666960.4310.40.camel@localhost.localdomain> <20061116011351.1401a00f.akpm@osdl.org> <1163708116.3737.12.camel@dyn9047017103.beaverton.ibm.com> <20061116132724.1882b122.akpm@osdl.org> <1164073652.20900.34.camel@dyn9047017103.beaverton.ibm.com> <1164156193.3804.48.camel@dyn9047017103.beaverton.ibm.com> Reply-To: cmm@us.ibm.com Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Mel Gorman , "Martin J. Bligh" , linux-kernel@vger.kernel.org, "linux-ext4@vger.kernel.org" Return-path: To: Andrew Morton , Hugh Dickins In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org ------------------------------------------------------ Subject: ext2 balloc: fix _with_rsv freeze From: Hugh Dickins 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 --- 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)) _