Date:   Thu, 21 Oct 2021 20:20:13 +0800
From:   Zhengyuan Liu <liuzhengyuang521@...il.com>
To:     yebin <yebin10@...wei.com>
Cc:     Jan Kara <jack@...e.cz>, viro@...iv.linux.org.uk,
        Andrew Morton <akpm@...ux-foundation.org>, tytso@....edu,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-ext4@...r.kernel.org,
        刘云 <liuyun01@...inos.cn>,
        Zhengyuan Liu <liuzhengyuan@...inos.cn>
Subject: Re: Problem with direct IO

On Thu, Oct 21, 2021 at 4:55 PM yebin <yebin10@...wei.com> wrote:
>
>
>
> On 2021/10/21 16:03, Jan Kara wrote:
>
> On Thu 21-10-21 10:21:55, Zhengyuan Liu wrote:
>
> On Thu, Oct 21, 2021 at 1:37 AM Jan Kara <jack@...e.cz> wrote:
>
> On Wed 13-10-21 09:46:46, Zhengyuan Liu wrote:
>
> we are encounting following Mysql crash problem while importing tables :
>
>     2021-09-26T11:22:17.825250Z 0 [ERROR] [MY-013622] [InnoDB] [FATAL]
>     fsync() returned EIO, aborting.
>     2021-09-26T11:22:17.825315Z 0 [ERROR] [MY-013183] [InnoDB]
>     Assertion failure: ut0ut.cc:555 thread 281472996733168
>
> At the same time , we found dmesg had following message:
>
>     [ 4328.838972] Page cache invalidation failure on direct I/O.
>     Possible data corruption due to collision with buffered I/O!
>     [ 4328.850234] File: /data/mysql/data/sysbench/sbtest53.ibd PID:
>     625 Comm: kworker/42:1
>
> Firstly, we doubled Mysql has operating the file with direct IO and
> buffered IO interlaced, but after some checking we found it did only
> do direct IO using aio. The problem is exactly from direct-io
> interface (__generic_file_write_iter) itself.
>
> ssize_t __generic_file_write_iter()
> {
> ...
>         if (iocb->ki_flags & IOCB_DIRECT) {
>                 loff_t pos, endbyte;
>
>                 written = generic_file_direct_write(iocb, from);
>                 /*
>                  * If the write stopped short of completing, fall back to
>                  * buffered writes.  Some filesystems do this for writes to
>                  * holes, for example.  For DAX files, a buffered write will
>                  * not succeed (even if it did, DAX does not handle dirty
>                  * page-cache pages correctly).
>                  */
>                 if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
>                         goto out;
>
>                 status = generic_perform_write(file, from, pos = iocb->ki_pos);
> ...
> }
>
> From above code snippet we can see that direct io could fall back to
> buffered IO under certain conditions, so even Mysql only did direct IO
> it could interleave with buffered IO when fall back occurred. I have
> no idea why FS(ext3) failed the direct IO currently, but it is strange
> __generic_file_write_iter make direct IO fall back to buffered IO, it
> seems  breaking the semantics of direct IO.
>
> The reproduced  environment is:
> Platform:  Kunpeng 920 (arm64)
> Kernel: V5.15-rc
> PAGESIZE: 64K
> Mysql:  V8.0
> Innodb_page_size: default(16K)
>
> Thanks for report. I agree this should not happen. How hard is this to
> reproduce? Any idea whether the fallback to buffered IO happens because
> iomap_dio_rw() returns -ENOTBLK or because it returns short write?
>
> It is easy to reproduce in my test environment, as I said in the previous
> email replied to Andrew this problem is related to kernel page size.
>
> Ok, can you share a reproducer?
>
> Can you post output of "dumpe2fs -h <device>" for the filesystem where the
> problem happens? Thanks!
>
> Sure, the output is:
>
> # dumpe2fs -h /dev/sda3
> dumpe2fs 1.45.3 (14-Jul-2019)
> Filesystem volume name:   <none>
> Last mounted on:          /data
> Filesystem UUID:          09a51146-b325-48bb-be63-c9df539a90a1
> Filesystem magic number:  0xEF53
> Filesystem revision #:    1 (dynamic)
> Filesystem features:      has_journal ext_attr resize_inode dir_index
> filetype needs_recovery sparse_super large_file
>
> Thanks for the data. OK, a filesystem without extents. Does your test by
> any chance try to do direct IO to a hole in a file? Because that is not
> (and never was) supported without extents. Also the fact that you don't see
> the problem with ext4 (which means extents support) would be pointing in
> that direction.
>
> Honza
>
>
> I try to reprodeuce this issue as follows, maybe this is just one scenario :
> step1:  Modify  kernel code, add delay in dio_complete and dio_bio_end_aio
> step2:  mkfs.ext4 /dev/sda
> step3:  mount /dev/sda  /home/test
> step4:  fio -filename=/home/test/test  -direct=0 -buffered=1 -iodepth 1 -thread -rw=write -rwmixread=70 -ioengine=libaio -bs=4k -size=16k -numjobs=1 -name=test_r_w
> step5:  fio -filename=/home/test/test  -direct=1 -buffered=0 -iodepth 1 -thread -rw=write -rwmixread=70 -ioengine=libaio -bs=4k -size=4k -numjobs=1 -name=test_r_w &
> step6:  fio -filename=/home/test/test  -direct=0 -buffered=1 -iodepth 1 -thread -rw=write -rwmixread=70 -ioengine=libaio -bs=4k -size=16k -numjobs=1 -name=test_r_w

Hi, yebin

Thanks for your test case,  but it is not the same problem. The scenario you
described here is some thing the kernel design for, since you are intending to
interleave buffered IO and direct IO, please look at this two patch:

332391a (“fs: Fix page cache inconsistency when mixing buffered and AIO DIO”)
5a9d929 (“iomap: report collisions between directio and buffered
writes to userspace”)

>
> Kernel modification base on v4.19:
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> +#include <linux/delay.h>
>
> /**
> @@ -305,6 +307,8 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, unsigned int flags)
>          * end_io() when necessary, otherwise a racing buffer read would cache
>          * zeros from unwritten extents.
>          */
> +       printk("%s: before invalidate page \n", __func__);
> +       mdelay(10 * 1000);
>         if (flags & DIO_COMPLETE_INVALIDATE &&
>             ret > 0 && dio->op == REQ_OP_WRITE &&
>             dio->inode->i_mapping->nrpages) {
> @@ -314,6 +318,7 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, unsigned int flags)
>                 if (err)
>                         dio_warn_stale_pagecache(dio->iocb->ki_filp);
>         }
> +       printk("%s: end invalidate page \n", __func__);
>
>         inode_dio_end(dio->inode);
>
> @@ -371,10 +378,17 @@ static void dio_bio_end_aio(struct bio *bio)
>                  * went in between AIO submission and completion into the
>                  * same region.
>                  */
> +               printk("%s:start to  sleep 5s.... \n", __func__);
> +               mdelay(10 * 1000);
> +               printk("%s: endto  sleep, defer_completion=%d op=%d nrpages=%d\n",
> +                       __func__,dio->defer_completion, dio->op, dio->inode->i_mapping->nrpages);
> +
>                 if (dio->result)
>                         defer_completion = dio->defer_completion ||
>                                            (dio->op == REQ_OP_WRITE &&
>                                             dio->inode->i_mapping->nrpages);
> +               printk("%s: dio=%px defer_completion=%d\n",
> +                       __func__, dio, defer_completion);
>                 if (defer_completion) {
>                         INIT_WORK(&dio->complete_work, dio_aio_complete_work);
>                         queue_work(dio->inode->i_sb->s_dio_done_wq,
>
>
> Reproduce result ：
> s=1 -name=test_r_w=write -rwmixread=70 -ioengine=libaio -bs=4k -size=16k -numjob
> test_r_w: (g=0): rw=write, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
> fio-3.7
> Starting 1 thread
> test_r_w: (groupid=0, jobs=1): err= 0: pid=2083: Sun Sep 26 03:18:06 2021
>   write: IOPS=444, BW=1778KiB/s (1820kB/s)(16.0KiB/9msec)
>     slat (usec): min=1294, max=3789, avg=2007.88, stdev=1191.07
>     clat (nsec): min=2304, max=28645, avg=9918.75, stdev=12574.80
>      lat (usec): min=1298, max=3824, avg=2020.36, stdev=1206.00
>     clat percentiles (nsec):
>      |  1.00th=[ 2320],  5.00th=[ 2320], 10.00th=[ 2320], 20.00th=[ 2320],
>      | 30.00th=[ 2960], 40.00th=[ 2960], 50.00th=[ 2960], 60.00th=[ 5792],
>      | 70.00th=[ 5792], 80.00th=[28544], 90.00th=[28544], 95.00th=[28544],
>      | 99.00th=[28544], 99.50th=[28544], 99.90th=[28544], 99.95th=[28544],
>      | 99.99th=[28544]
>   lat (usec)   : 4=50.00%, 10=25.00%, 50=25.00%
>   cpu          : usr=0.00%, sys=87.50%, ctx=0, majf=0, minf=1
>   IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
>      submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
>      complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
>      issued rwts: total=0,4,0,0 short=0,0,0,0 dropped=0,0,0,0
>      latency   : target=0, window=0, percentile=100.00%, depth=1
>
> Run status group 0 (all jobs):
>   WRITE: bw=1778KiB/s (1820kB/s), 1778KiB/s-1778KiB/s (1820kB/s-1820kB/s), io=16.0KiB (16.4kB), run=9-9msec
>
> Disk stats (read/write):
>   sda: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%
> =1 -name=test_r_w &write -rwmixread=70 -ioengine=libaio -bs=4k -size=4k -numjobs
> [1] 2087
> [root@...alhost home]# test_r_w: (g=0): rw=write, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
> fio-3.7
> Starting 1 thread
>
> [root@...alhost home]# [ 1475.286928] ext4_file_write_iter: start lock inode
> [ 1475.288807] ext4_file_write_iter: unlock inode
> [ 1475.290402] dio_bio_end_aio:start to  sleep 5s....
>
> s=1 -name=test_r_w=write -rwmixread=70 -ioengine=libaio -bs=4k -size=16k -numjob
> test_r_w: (g=0): rw=write, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
> fio-3.7
> Starting 1 thread
> Jobs: 1 (f=0): [f(1)][-.-%][r=0KiB/s,w=0KiB/s][r=0,w=0 IOPS][eta 00m:00s]
> Jobs: 1 (f=0): [f(1)][-.-%][r=0KiB/s,w=0KiB/s][r=0,w=0 IOPS][eta 00m:00s]
> [ 1485.292939] dio_bio_end_aio: endto  sleep, defer_completion=0 op=1 nrpages=4
> [ 1485.293888] dio_bio_end_aio: dio=ffff88839aff5200 defer_completion=1
> [ 1485.294821] dio_aio_complete_work: dio=ffff88839aff5200...
> Jobs: 1 (f=1): [W(1)][-.-%][r=0KiB/s,w=0KiB/s][r[ 1485.296539] dio_complete: before invalidate page
> [ 1495.298472] Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!     -->detect  buffer io and direct io conflict.
> [ 1495.302746] File: /home/test/test PID: 493 Comm: kworker/3:2
> [ 1495.303508] CPU: 3 PID: 493 Comm: kworker/3:2 Not tainted 4.19.90-dirty #96
> [ 1495.304386] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
> Jobs: 1 (f=1): [[ 1495.306050] Workqueue: dio/sda dio_aio_complete_work
> W(1)][-.-%][r=0K
> [ 1495.316879] dio_complete: end invalidate page
> test_r_w: (groupid=0, jobs=1): err= 0: pid=2092: Sun Sep 26 03:18:37 2021
>   write: IOPS=266, BW=1067KiB/s (1092kB/s)(16.0KiB/15msec)
>     slat (usec): min=2001, max=3101, avg=2691.97, stdev=480.07
>     clat (nsec): min=2058, max=12337, avg=5999.50, stdev=4456.54
>      lat (usec): min=2004, max=3116, avg=2700.11, stdev=484.22
>     clat percentiles (nsec):
>      |  1.00th=[ 2064],  5.00th=[ 2064], 10.00th=[ 2064], 20.00th=[ 2064],
>      | 30.00th=[ 4080], 40.00th=[ 4080], 50.00th=[ 4080], 60.00th=[ 5536],
>      | 70.00th=[ 5536], 80.00th=[12352], 90.00th=[12352], 95.00th=[12352],
>      | 99.00th=[12352], 99.50th=[12352], 99.90th=[12352], 99.95th=[12352],
>      | 99.99th=[12352]
>   lat (usec)   : 4=25.00%, 10=50.00%, 20=25.00%
>   cpu          : usr=0.00%, sys=100.00%, ctx=1, majf=0, minf=1
>   IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
>      submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
>      complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
>      issued rwts: total=0,4,0,0 short=0,0,0,0 dropped=0,0,0,0
>      latency   : target=0, window=0, percentile=100.00%, depth=1
>
> Run status group 0 (all jobs):
>   WRITE: bw=1067KiB/s (1092kB/s), 1067KiB/s-1067KiB/s (1092kB/s-1092kB/s), io=16.0KiB (16.4kB), run=15-15msec
>
> Disk stats (read/write):
>   sda: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%
>
> test_r_w: (groupid=0, jobs=1): err= 0: pid=2089: Sun Sep 26 03:18:37 2021
>   write: IOPS=0, BW=204B/s (204B/s)(4096B/20033msec)
>     slat (nsec): min=3358.7k, max=3358.7k, avg=3358748.00, stdev= 0.00
>     clat (nsec): min=20027M, max=20027M, avg=20027265355.00, stdev= 0.00
>      lat (nsec): min=20031M, max=20031M, avg=20030627283.00, stdev= 0.00
>     clat percentiles (msec):
>      |  1.00th=[17113],  5.00th=[17113], 10.00th=[17113], 20.00th=[17113],
>      | 30.00th=[17113], 40.00th=[17113], 50.00th=[17113], 60.00th=[17113],
>      | 70.00th=[17113], 80.00th=[17113], 90.00th=[17113], 95.00th=[17113],
>      | 99.00th=[17113], 99.50th=[17113], 99.90th=[17113], 99.95th=[17113],
>      | 99.99th=[17113]
>   cpu          : usr=0.00%, sys=0.02%, ctx=2, majf=0, minf=1
>   IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
>      submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
>      complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
>      issued rwts: total=0,1,0,0 short=0,0,0,0 dropped=0,0,0,0
>      latency   : target=0, window=0, percentile=100.00%, depth=1
>
> Run status group 0 (all jobs):
>   WRITE: bw=204B/s (204B/s), 204B/s-204B/s (204B/s-204B/s), io=4096B (4096B), run=20033-20033msec
>
> Disk stats (read/write):
>   sda: ios=0/5, merge=0/1, ticks=0/10018, in_queue=10015, util=36.98%
>
>
>

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