On Fri, 18 Jan 2013 13:00:38 +0100, Jan Kara <jack@xxxxxxx> wrote: > Merging of uninitialized extents creates all sorts of interesting race > possibilities when writeback / DIO races with fallocate. Thus > ext4_convert_unwritten_extents_endio() has to deal with a case where > extent to be converted needs to be split out first. That isn't nice > for two reasons: > > 1) It may need allocation of extent tree block so ENOSPC is possible. > 2) It complicates end_io handling code As we already discussed your idea is 100% correct, but even with what patch I still able to trigger situation where split it required. I've got following error with this patch applied on top of 7f5118629f7 EXT4-fs error (device dm-3): ext4_convert_unwritten_extents_endio:3411: inode #12: comm kworker/u:4: Written extent modified before IO finished: extent logical block 1379787, len 64; IO logical block 1379787, len 21 ------------[ cut here ]------------ WARNING: at fs/ext4/extents.c:4518 ext4_convert_unwritten_extents+0x149/0x210 [ext4]() Hardware name: Modules linked in: ext4 jbd2 cpufreq_ondemand acpi_cpufreq freq_table mperf coretemp kvm_intel kvm crc32c_intel microcode sg button ext3 jbd mbcache sd_mod crc_t10dif ahci libahci pata_acpi ata_generic dm_mirror dm_region_hash dm_log dm_mod Pid: 249, comm: kworker/u:4 Not tainted 3.8.0-rc3+ #16 Call Trace: [<ffffffff8106fc23>] warn_slowpath_common+0xc3/0xf0 [<ffffffff8106fc6a>] warn_slowpath_null+0x1a/0x20 [<ffffffffa03fb909>] ext4_convert_unwritten_extents+0x149/0x210 [ext4] [<ffffffff811064fa>] ? __lock_release+0x1da/0x1f0 [<ffffffffa03c368e>] ext4_end_io+0x3e/0x160 [ext4] [<ffffffff813aab40>] ? __list_del_entry+0x210/0x250 [<ffffffffa03c3a21>] ext4_do_flush_completed_IO+0x101/0x280 [ext4] [<ffffffffa03c3bb6>] ext4_end_io_work+0x16/0x20 [ext4] [<ffffffff8109f7dd>] process_one_work+0x4ad/0x780 [<ffffffff8109f6d2>] ? process_one_work+0x3a2/0x780 [<ffffffffa03c3ba0>] ? ext4_do_flush_completed_IO+0x280/0x280 [ext4] [<ffffffff810a3ed1>] worker_thread+0x3f1/0x590 [<ffffffff810a3ae0>] ? manage_workers+0x210/0x210 [<ffffffff810ac870>] kthread+0x100/0x110 [<ffffffff810ac770>] ? __init_kthread_worker+0x70/0x70 [<ffffffff81812e2c>] ret_from_fork+0x7c/0xb0 [<ffffffff810ac770>] ? __init_kthread_worker+0x70/0x70 ---[ end trace add5cefed72186f8 ]--- EXT4-fs (dm-3): ext4_convert_unwritten_extents:4522: inode #12: block 1379787: len 21: ext4_ext_map_blocks returned -5 EXT4-fs (dm-3): failed to convert unwritten extents to written extents -- potential data loss! (inode 12, offset 5651562496, size 131072, error -5) I've run 286'th xfstest (this is my own copy of xfstest so 286'th test is differ from mainstream one) you can find it here https://raw.github.com/dmonakhov/xfstests/devel/286 In two words it is stress test which run DIO/AIO,truncate,fallocate in parallel. Also you need recent FIO(http://git.kernel.dk/?p=fio.git;a=summary) Currently I try to understand what caused this issue. > > So we disable merging of uninitialized extents which allows us to simplify > the code. Extents will get merged after they are converted to initialized > ones. > > Reviewed-by: Zheng Liu <wenqing.lz@xxxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> > --- > fs/ext4/extents.c | 61 +++++++++++++++------------------------------------- > 1 files changed, 18 insertions(+), 43 deletions(-) > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > index 26af228..f1ce33a 100644 > --- a/fs/ext4/extents.c > +++ b/fs/ext4/extents.c > @@ -54,9 +54,6 @@ > #define EXT4_EXT_MARK_UNINIT1 0x2 /* mark first half uninitialized */ > #define EXT4_EXT_MARK_UNINIT2 0x4 /* mark second half uninitialized */ > > -#define EXT4_EXT_DATA_VALID1 0x8 /* first half contains valid data */ > -#define EXT4_EXT_DATA_VALID2 0x10 /* second half contains valid data */ > - > static __le32 ext4_extent_block_csum(struct inode *inode, > struct ext4_extent_header *eh) > { > @@ -1579,20 +1576,17 @@ int > ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1, > struct ext4_extent *ex2) > { > - unsigned short ext1_ee_len, ext2_ee_len, max_len; > + unsigned ext1_ee_len, ext2_ee_len; > > /* > - * Make sure that either both extents are uninitialized, or > - * both are _not_. > + * Make sure that both extents are initialized. We don't merge > + * uninitialized extents so that we can be sure that end_io code has > + * the extent that was written properly split out and conversion to > + * initialized is trivial. > */ > - if (ext4_ext_is_uninitialized(ex1) ^ ext4_ext_is_uninitialized(ex2)) > + if (ext4_ext_is_uninitialized(ex1) || ext4_ext_is_uninitialized(ex2)) > return 0; > > - if (ext4_ext_is_uninitialized(ex1)) > - max_len = EXT_UNINIT_MAX_LEN; > - else > - max_len = EXT_INIT_MAX_LEN; > - > ext1_ee_len = ext4_ext_get_actual_len(ex1); > ext2_ee_len = ext4_ext_get_actual_len(ex2); > > @@ -1605,7 +1599,7 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1, > * as an RO_COMPAT feature, refuse to merge to extents if > * this can result in the top bit of ee_len being set. > */ > - if (ext1_ee_len + ext2_ee_len > max_len) > + if (ext1_ee_len + ext2_ee_len > EXT_INIT_MAX_LEN) > return 0; > #ifdef AGGRESSIVE_TEST > if (ext1_ee_len >= 4) > @@ -2959,9 +2953,6 @@ static int ext4_split_extent_at(handle_t *handle, > unsigned int ee_len, depth; > int err = 0; > > - BUG_ON((split_flag & (EXT4_EXT_DATA_VALID1 | EXT4_EXT_DATA_VALID2)) == > - (EXT4_EXT_DATA_VALID1 | EXT4_EXT_DATA_VALID2)); > - > ext_debug("ext4_split_extents_at: inode %lu, logical" > "block %llu\n", inode->i_ino, (unsigned long long)split); > > @@ -3020,14 +3011,7 @@ static int ext4_split_extent_at(handle_t *handle, > > err = ext4_ext_insert_extent(handle, inode, path, &newex, flags); > if (err == -ENOSPC && (EXT4_EXT_MAY_ZEROOUT & split_flag)) { > - if (split_flag & (EXT4_EXT_DATA_VALID1|EXT4_EXT_DATA_VALID2)) { > - if (split_flag & EXT4_EXT_DATA_VALID1) > - err = ext4_ext_zeroout(inode, ex2); > - else > - err = ext4_ext_zeroout(inode, ex); > - } else > - err = ext4_ext_zeroout(inode, &orig_ex); > - > + err = ext4_ext_zeroout(inode, &orig_ex); > if (err) > goto fix_extent_len; > /* update the extent length and mark as initialized */ > @@ -3085,8 +3069,6 @@ static int ext4_split_extent(handle_t *handle, > if (uninitialized) > split_flag1 |= EXT4_EXT_MARK_UNINIT1 | > EXT4_EXT_MARK_UNINIT2; > - if (split_flag & EXT4_EXT_DATA_VALID2) > - split_flag1 |= EXT4_EXT_DATA_VALID1; > err = ext4_split_extent_at(handle, inode, path, > map->m_lblk + map->m_len, split_flag1, flags1); > if (err) > @@ -3099,8 +3081,7 @@ static int ext4_split_extent(handle_t *handle, > return PTR_ERR(path); > > if (map->m_lblk >= ee_block) { > - split_flag1 = split_flag & (EXT4_EXT_MAY_ZEROOUT | > - EXT4_EXT_DATA_VALID2); > + split_flag1 = split_flag & EXT4_EXT_MAY_ZEROOUT; > if (uninitialized) > split_flag1 |= EXT4_EXT_MARK_UNINIT1; > if (split_flag & EXT4_EXT_MARK_UNINIT2) > @@ -3379,8 +3360,7 @@ static int ext4_split_unwritten_extents(handle_t *handle, > > split_flag |= ee_block + ee_len <= eof_block ? EXT4_EXT_MAY_ZEROOUT : 0; > split_flag |= EXT4_EXT_MARK_UNINIT2; > - if (flags & EXT4_GET_BLOCKS_CONVERT) > - split_flag |= EXT4_EXT_DATA_VALID2; > + > flags |= EXT4_GET_BLOCKS_PRE_IO; > return ext4_split_extent(handle, inode, path, map, split_flag, flags); > } > @@ -3405,20 +3385,15 @@ static int ext4_convert_unwritten_extents_endio(handle_t *handle, > "block %llu, max_blocks %u\n", inode->i_ino, > (unsigned long long)ee_block, ee_len); > > - /* If extent is larger than requested then split is required */ > + /* Extent is larger than requested? */ > if (ee_block != map->m_lblk || ee_len > map->m_len) { > - err = ext4_split_unwritten_extents(handle, inode, map, path, > - EXT4_GET_BLOCKS_CONVERT); > - if (err < 0) > - goto out; > - ext4_ext_drop_refs(path); > - path = ext4_ext_find_extent(inode, map->m_lblk, path); > - if (IS_ERR(path)) { > - err = PTR_ERR(path); > - goto out; > - } > - depth = ext_depth(inode); > - ex = path[depth].p_ext; > + EXT4_ERROR_INODE(inode, "Written extent modified before IO" > + " finished: extent logical block %llu, len %u; IO" > + " logical block %llu, len %u\n", > + (unsigned long long)ee_block, ee_len, > + (unsigned long long)map->m_lblk, map->m_len); > + err = -EIO; > + goto out; > } > > err = ext4_ext_get_access(handle, inode, path + depth); > -- > 1.7.1 > > -- > 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 -- 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
