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Subject: Re: Writes stoped working on f2fs after the compression support was
 added
To:     Jaegeuk Kim <jaegeuk@kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
References: <20191209222345.1078-1-jaegeuk@kernel.org>
 <20200222044617.pfrhnz2iavkrtdn6@core.my.home>
 <20200222181721.tzrrohep5l3yklpf@core.my.home>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <bec3798b-f861-b132-9138-221027bb5195@huawei.com>
Date:   Mon, 24 Feb 2020 18:37:41 +0800
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Hi,

Thanks for the report.

On 2020/2/23 2:17, Ondřej Jirman wrote:
> Hello,
> 
> I observe hung background f2fs task on 5.6-rc2+ shortly after boot, leading to
> panics. I use f2fs as rootfs. See below for stack trace. The reads continue to
> work (if I disable panic on hung task). But sync blocks, writes block, etc.
> 
> It does not happen on all my f2fs filesystems, so it may depend on workload
> or my particular filesystem state. It happens on two separate devices though,
> both 32-bit, and doesn't happen on a 64-bit device. (might be a false lead,
> though)
> 
> I went through the f2fs-for-5.6 tag/branch and reverted each patch right
> down to:
> 
>   4c8ff7095bef64fc47e996a938f7d57f9e077da3 f2fs: support data compression
> 
> I could still reproduce the issue.
> 
> After reverting the data compression too, I could no longer reproduce the
> issue. Perhaps not very helpful, since that patch is huge.
> 
> I tried to collect some information. Some ftrace logs, etc. Not sure what would
> help debug this. Let me know if I can help debug this more.
> 
> Symptoms look the same as this issue:
> 
>   https://www.mail-archive.com/linux-f2fs-devel@lists.sourceforge.net/msg15298.html
> 
> ftrace: https://megous.com/dl/tmp/f2fs-debug-info.txt
> 
> longer ftrace: https://megous.com/dl/tmp/f2fs-debug-info-full.txt

I checked the full trace log, however I didn't find any clue to troubleshot this issue.

[snip]

> dmesg:

Could you dump all other task stack info via "echo "t" > /proc/sysrq-trigger"?

> 
> [  246.758021] INFO: task kworker/u16:1:58 blocked for more than 122 seconds.
> [  246.758040]       Not tainted 5.6.0-rc2-00590-g9983bdae4974e #11
> [  246.758044] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [  246.758052] kworker/u16:1   D    0    58      2 0x00000000
> [  246.758090] Workqueue: writeback wb_workfn (flush-179:0)
> [  246.758099] Backtrace:
> [  246.758121] [<c0912b90>] (__schedule) from [<c0913234>] (schedule+0x78/0xf4)
> [  246.758130]  r10:da644000 r9:00000000 r8:da645a60 r7:da283e10 r6:00000002 r5:da644000
> [  246.758132]  r4:da4d3600
> [  246.758148] [<c09131bc>] (schedule) from [<c017ec74>] (rwsem_down_write_slowpath+0x24c/0x4c0)
> [  246.758152]  r5:00000001 r4:da283e00
> [  246.758161] [<c017ea28>] (rwsem_down_write_slowpath) from [<c0915f2c>] (down_write+0x6c/0x70)
> [  246.758167]  r10:da283e00 r9:da645d80 r8:d9ed0000 r7:00000001 r6:00000000 r5:eff213b0
> [  246.758169]  r4:da283e00
> [  246.758187] [<c0915ec0>] (down_write) from [<c0435b80>] (f2fs_write_single_data_page+0x608/0x7ac)

I'm not sure what is this semaphore, I suspect this is F2FS_I(inode)->i_sem, in order to make
sure of this, can you help to add below function, and use them to replace
all {down,up}_{write,read}(&.i_sem) invoking? then reproduce this issue and catch the log.

Thanks,

> [  246.758190]  r5:eff213b0 r4:da283c60
> [  246.758198] [<c0435578>] (f2fs_write_single_data_page) from [<c0435fd8>] (f2fs_write_cache_pages+0x2b4/0x7c4)
> [  246.758204]  r10:da645c28 r9:da283d60 r8:da283c60 r7:0000000f r6:da645d80 r5:00000001
> [  246.758206]  r4:eff213b0
> [  246.758214] [<c0435d24>] (f2fs_write_cache_pages) from [<c043682c>] (f2fs_write_data_pages+0x344/0x35c)
> [  246.758220]  r10:00000000 r9:d9ed002c r8:d9ed0000 r7:00000004 r6:da283d60 r5:da283c60
> [  246.758223]  r4:da645d80
> [  246.758238] [<c04364e8>] (f2fs_write_data_pages) from [<c0267ee8>] (do_writepages+0x3c/0xd4)
> [  246.758244]  r10:0000000a r9:c0e03d00 r8:00000c00 r7:c0264ddc r6:da645d80 r5:da283d60
> [  246.758246]  r4:da283c60
> [  246.758254] [<c0267eac>] (do_writepages) from [<c0310cbc>] (__writeback_single_inode+0x44/0x454)
> [  246.758259]  r7:da283d60 r6:da645eac r5:da645d80 r4:da283c60
> [  246.758266] [<c0310c78>] (__writeback_single_inode) from [<c03112d0>] (writeback_sb_inodes+0x204/0x4b0)
> [  246.758272]  r10:0000000a r9:c0e03d00 r8:da283cc8 r7:da283c60 r6:da645eac r5:da283d08
> [  246.758274]  r4:d9dc9848
> [  246.758281] [<c03110cc>] (writeback_sb_inodes) from [<c03115cc>] (__writeback_inodes_wb+0x50/0xe4)
> [  246.758287]  r10:da3797a8 r9:c0e03d00 r8:d9dc985c r7:da645eac r6:00000000 r5:d9dc9848
> [  246.758289]  r4:da5a8800
> [  246.758296] [<c031157c>] (__writeback_inodes_wb) from [<c03118f4>] (wb_writeback+0x294/0x338)
> [  246.758302]  r10:fffbf200 r9:da644000 r8:c0e04e64 r7:d9dc9848 r6:d9dc9874 r5:da645eac
> [  246.758305]  r4:d9dc9848
> [  246.758312] [<c0311660>] (wb_writeback) from [<c0312dac>] (wb_workfn+0x35c/0x54c)
> [  246.758318]  r10:da5f2005 r9:d9dc984c r8:d9dc9948 r7:d9dc9848 r6:00000000 r5:d9dc9954
> [  246.758321]  r4:000031e6
> [  246.758334] [<c0312a50>] (wb_workfn) from [<c014f2b8>] (process_one_work+0x214/0x544)
> [  246.758340]  r10:da5f2005 r9:00000200 r8:00000000 r7:da5f2000 r6:ef044400 r5:da5eb000
> [  246.758343]  r4:d9dc9954
> [  246.758350] [<c014f0a4>] (process_one_work) from [<c014f634>] (worker_thread+0x4c/0x574)
> [  246.758357]  r10:ef044400 r9:c0e03d00 r8:ef044418 r7:00000088 r6:ef044400 r5:da5eb014
> [  246.758359]  r4:da5eb000
> [  246.758368] [<c014f5e8>] (worker_thread) from [<c01564fc>] (kthread+0x144/0x170)
> [  246.758374]  r10:ec9e5e90 r9:dabf325c r8:da5eb000 r7:da644000 r6:00000000 r5:da5fe000
> [  246.758377]  r4:dabf3240
> [  246.758386] [<c01563b8>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
> [  246.758391] Exception stack(0xda645fb0 to 0xda645ff8)
> [  246.758397] 5fa0:                                     00000000 00000000 00000000 00000000
> [  246.758402] 5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> [  246.758407] 5fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> [  246.758413]  r10:00000000 r9:00000000 r8:00000000 r7:00000000 r6:00000000 r5:c01563b8
> [  246.758416]  r4:da5fe000
> .
>