From ad4fb9cafe100a4a9de6e0529015e584d94ac8dc Mon Sep 17 00:00:00 2001 From: Kazuya Mio Date: Mon, 10 Jan 2011 12:12:28 -0500 Subject: [PATCH] ext4: fix 32bit overflow in ext4_ext_find_goal() ext4_ext_find_goal() returns an ideal physical block number that the block allocator tries to allocate first. However, if a required file offset is smaller than the existing extent's one, ext4_ext_find_goal() returns a wrong block number because it may overflow at "block - le32_to_cpu(ex->ee_block)". This patch fixes the problem. ext4_ext_find_goal() will also return a wrong block number in case a file offset of the existing extent is too big. In this case, the ideal physical block number is fixed in ext4_mb_initialize_context(), so it's no problem. reproduce: # dd if=/dev/zero of=/mnt/mp1/tmp bs=127M count=1 oflag=sync # dd if=/dev/zero of=/mnt/mp1/file bs=512K count=1 seek=1 oflag=sync # filefrag -v /mnt/mp1/file Filesystem type is: ef53 File size of /mnt/mp1/file is 1048576 (256 blocks, blocksize 4096) ext logical physical expected length flags 0 128 67456 128 eof /mnt/mp1/file: 2 extents found # rm -rf /mnt/mp1/tmp # echo $((512*4096)) > /sys/fs/ext4/loop0/mb_stream_req # dd if=/dev/zero of=/mnt/mp1/file bs=512K count=1 oflag=sync conv=notrunc result (linux-2.6.37-rc2 + ext4 patch queue): # filefrag -v /mnt/mp1/file Filesystem type is: ef53 File size of /mnt/mp1/file is 1048576 (256 blocks, blocksize 4096) ext logical physical expected length flags 0 0 33280 128 1 128 67456 33407 128 eof /mnt/mp1/file: 2 extents found result(apply this patch): # filefrag -v /mnt/mp1/file Filesystem type is: ef53 File size of /mnt/mp1/file is 1048576 (256 blocks, blocksize 4096) ext logical physical expected length flags 0 0 66560 128 1 128 67456 66687 128 eof /mnt/mp1/file: 2 extents found Signed-off-by: Kazuya Mio Signed-off-by: "Theodore Ts'o" --- fs/ext4/extents.c | 30 ++++++++++++++++++++++++++---- 1 file changed, 26 insertions(+), 4 deletions(-) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 0554c48..d53e20f 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -117,11 +117,33 @@ static ext4_fsblk_t ext4_ext_find_goal(struct inode *inode, struct ext4_extent *ex; depth = path->p_depth; - /* try to predict block placement */ + /* + * Try to predict block placement assuming that we are + * filling in a file which will eventually be + * non-sparse --- i.e., in the case of libbfd writing + * an ELF object sections out-of-order but in a way + * the eventually results in a contiguous object or + * executable file, or some database extending a table + * space file. However, this is actually somewhat + * non-ideal if we are writing a sparse file such as + * qemu or KVM writing a raw image file that is going + * to stay fairly sparse, since it will end up + * fragmenting the file system's free space. Maybe we + * should have some hueristics or some way to allow + * userspace to pass a hint to file system, + * especiially if the latter case turns out to be + * common. + */ ex = path[depth].p_ext; - if (ex) - return (ext4_ext_pblock(ex) + - (block - le32_to_cpu(ex->ee_block))); + if (ex) { + ext4_fsblk_t ext_pblk = ext4_ext_pblock(ex); + ext4_lblk_t ext_block = le32_to_cpu(ex->ee_block); + + if (block > ext_block) + return ext_pblk + (block - ext_block); + else + return ext_pblk - (ext_block - block); + } /* it looks like index is empty; * try to find starting block from index itself */ -- 2.7.4