On Wed, 15 Nov 2006 14:17:01 +0000 (GMT) Hugh Dickins <hugh@xxxxxxxxxxx> wrote: > On Tue, 14 Nov 2006, Hugh Dickins wrote: > > On Tue, 14 Nov 2006, Andrew Morton wrote: > > > > > > The below might help. > > > > Indeed it does (with Martin's E2FSBLK warning fix), > > seems to be running well on all machines now. > > i386 and ppc64 still doing builds, but after an hour on x86_64, > an ld got stuck in a loop under ext2_try_to_allocate_with_rsv, > alternating between ext2_rsv_window_add and rsv_window_remove. > Send me a patch and I'll try it... > > ext2_try_to_allocate_with_rsv+0x288 > ext2_new_blocks+0x21e > ext2_get_blocks+0x398 > ext2_get_block+0x46 > __block_prepare_write+0x171 > block_prepare_write+0x39 > ext2_prepare_write+0x2c > generic_file_buffered_write+0x2b0 > __generic_file_aio_write_nolock+0x4bc > generic_file_aio_write+0x6d > do_sync_write+0xf9 > vfs_write+0xc8 > sys_write+0x51 OK, I have a theory. This must have been the seventeenth damn time I've stared at find_next_zero_bit() wondering what the damn return value is and wondering how any even slightly non-sadistic person could write a damn function like that and not damn well document it. int find_next_zero_bit(const unsigned long *addr, int size, int offset) It returns the offset of the first zero bit relative to addr. ext3's bitmap_search_next_usable_block() assumed that find_next_zero_bit() returns the offset of the first zero bit relative to (addr+offset). The while loop in ext3's bitmap_search_next_usable_block() serendipitously covered that bug up. ext2's bitmap_search_next_usable_block() doesn't need that while loop, so ext3's benign bug became ext2's fatal bug. So... --- a/fs/ext2/balloc.c~a +++ a/fs/ext2/balloc.c @@ -524,7 +524,7 @@ bitmap_search_next_usable_block(ext2_grp ext2_grpblk_t next; next = ext2_find_next_zero_bit(bh->b_data, maxblocks, start); - if (next >= maxblocks) + if (next >= start + maxblocks) return -1; return next; } _ Anyway, I think that's the bug. Or a bug, at least. If so, the cause of this bug is inadequate code commenting, pure and simple. And ext3 and ext4 need fixing. - 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
