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Date: Thu, 24 Jan 2013 19:32:22 +0400
From: Dmitry Monakhov <dmonakhov@...nvz.org>
To: Jan Kara <jack@...e.cz>
Cc: Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH 04/12] ext4: Disable merging of uninitialized extents
On Thu, 24 Jan 2013 16:12:24 +0100, Jan Kara <jack@...e.cz> wrote:
> On Thu 24-01-13 13:49:45, Dmitry Monakhov wrote:
> > On Fri, 18 Jan 2013 13:00:38 +0100, Jan Kara <jack@...e.cz> 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
> Drat, thanks for heads up. I did run xfstests on the patch set but
> apparently you are doing something more evil :) If I get your test & error
> right, you do AIO DIO to a file while doing truncate 0, fallocate SIZE, in
> a loop. And extent is found longer when we finish the IO. Am I right?
Correct. AFAIU we have another bug which break things
I've added prink for ext4_can_extents_be_merged if it was positive
And have got following output: lblk len pblk uninit lblk len pblk uninit
ext4_can_extents_be_merged:1618 ex1[2254944:32, 2052192]:0 ex2[2254976:32, 2052224]:0
ext4_can_extents_be_merged:1618 ex1[398176:32, 2198368]:0 ex2[398208:32,2198400]:0
ext4_can_extents_be_merged:1618 ex1[584704:32, 1379328]:0 ex2[584736:32,1379360]:0
ext4_can_extents_be_merged:1618 ex1[1407488:32, 762368]:0 ex2[1407520:32, 762400]:0
ext4_can_extents_be_merged:1618 ex1[443744:32, 2495456]:0 ex2[443776:32,2495488]:0
ext4_can_extents_be_merged:1618 ex1[1057230:1, 2190944]:0 ex2[1057231:17, 2190945]:0
ext4_can_extents_be_merged:1618 ex1[2108160:832, 2563328]:0 ex2[2108992:32, 2564160]:0
##### Here Both extents was initialized ^^^ ^^^
EXT4-fs error (device dm-3): ext4_convert_unwritten_extents_endio:3426: inode #12: comm kworker/u:4: Written extent modif
ied before IO finished: extent logical block 2108576, len 448; IO logical block 2108576, len 32
#####But right after that it is appeared uninitialized.
>
> Honza
> > ------------[ 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@...bao.com>
> > > Signed-off-by: Jan Kara <jack@...e.cz>
> > > ---
> > > 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@...r.kernel.org
> > > More majordomo info at http://vger.kernel.org/majordomo-info.html
> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
> --
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