[Ocfs2-devel] Fwd: Re: [PATCH v2 0/4] ocfs2: seq_file .next functions should increase position index

Fri Mar 20 21:24:52 PDT 2020

test environment:
	kernel version: 5.6.0-rc5

lockres_seq_next -->
/sys/kernel/debug/o2dlm/2C9B43EBE44D4715A0B0DBE4D72016A3/locking_state
The output content is incomplete and endless, and the subsequent output is skip reading.
The operation and print is as follows:
dd if=/sys/kernel/debug/o2dlm/2C9B43EBE44D4715A0B0DBE4D72016A3/locking_state bs=40 skip=1
S:1,5,0,0,0,0,0,0,0,0,3
RMAP:
LVBX:00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
LOCK:1,0,5,-1,5,5:1,0,0,0,0,0,0,0,0,2

NAME:M0000000000000000000042e7349704
LRES:1,5,0,0,0,0,0,0,0,0,3
RMAP:
LVBX:00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
LOCK:1,0,5,-1,5,5:2,0,0,0,0,0,0,0,0,2
........
NAME:M0000000000000000000042e7349704
LRES:1,5,0,0,0,0,0,0,0,0,3
RMAP:
LVBX:00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
LOCK:1,0,5,-1,5,5:2,0,0,0,0,0,0,0,0,2

NAME:M0000000000000000000010e7349704
......

but, there is no endless output using the following script:
linux-EalnPD:~ # q=;while read -r r;do echo "$((++q)) $r";done < /sys/kernel/debug/o2dlm/2C9B43EBE44D4715A0B0DBE4D72016A3/locking_state
1 NAME:S000000000000000000000200000000
2 LRES:1,5,0,0,0,0,0,0,0,0,3
3 RMAP:
4 LVBX:00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
5 LOCK:1,0,5,-1,5,5:6,0,0,0,0,0,0,0,0,2
6
7
8 NAME:M0000000000000000000016e7349704
9 NAME:M0000000000000000000018e7349704
10 NAME:M000000000000000000001ae7349704
11 NAME:M000000000000000000001ce7349704
12 NAME:M000000000000000000001ee7349704
13 NAME:M0000000000000000000020e7349704
....
534 NAME:W00000000000000000843c81d0b7768
535 NAME:O00000000000000000843c800000000

Other interface test results:
nst_seq_next --> /sys/kernel/debug/o2net/send_tracking
sc_seq_next --> /sys/kernel/debug/o2net/stats
File content is empty, so, read it like use dd command, No effect.
ocfs2_dlm_seq_next -->
/sys/kernel/debug/ocfs2/2C9B43EBE44D4715A0B0DBE4D72016A3/locking_state
Read file normal output.

And, output is still endless, after adding Vasily Averin's modifications, patch are as follow:
[Ocfs2-devel] [PATCH v2 1/4] lockres_seq_next should increase position index   Vasily Averin
[Ocfs2-devel] [PATCH v2 2/4] ocfs2_dlm_seq_next should increase position index   Vasily Averin
[Ocfs2-devel] [PATCH v2 3/4] nst_seq_next should increase position index   Vasily Averin
[Ocfs2-devel] [PATCH v2 4/4] sc_seq_next should increase position index

I added the log in seq_read, use the 'dd' read command above, print as follows:
2020-03-21T11:27:50.691302+08:00|notice|kernel[-]|[92756.285422] [22000/dd] --> seq_read, init, start ppos 250434, max read size 10, m->read_pos 250434, mem index 1028, mem size 4096, mem from 233, mem count 11.
2020-03-21T11:27:50.691328+08:00|notice|kernel[-]|[92756.285430] [22000/dd] --> seq_read, init, start ppos 250444, max read size 10, m->read_pos 250444, mem index 1028, mem size 4096, mem from 243, mem count 1.
2020-03-21T11:27:50.691355+08:00|notice|kernel[-]|[92756.285442] [22000/dd] --> seq_read, read start, m->read_pos 250444, mem index 1028, mem size 4096, mem from 0, mem count 0.
2020-03-21T11:27:50.691381+08:00|notice|kernel[-]|[92756.285444] [22000/dd] --> seq_read, before go to file, mem file count 244, mem file size 4096
2020-03-21T11:27:50.691406+08:00|notice|kernel[-]|[92756.285453] [22000/dd] --> seq_read, init, start ppos 250454, max read size 10, m->read_pos 250454, mem index 1029, mem size 4096, mem from 9, mem count 235.
2020-03-21T11:27:50.691434+08:00|notice|kernel[-]|[92756.285458] [22000/dd] --> seq_read, init, start ppos 250464, max read size 10, m->read_pos 250464, mem index 1029, mem size 4096, mem from 19, mem count 225.
......

I haven't figured out what the reason is, but the result is not as expected.

On 2020/3/9 16:27, piaojun wrote:
> 
> 
> 
> -------- Forwarded Message --------
> Subject: Re: [PATCH v2 0/4] ocfs2: seq_file .next functions should increase position index
> Date: Wed, 26 Feb 2020 16:32:30 +0800
> From: Joseph Qi <joseph.qi at linux.alibaba.com>
> To: Vasily Averin <vvs at virtuozzo.com>, ocfs2-devel at oss.oracle.com, piaojun <piaojun at huawei.com>
> CC: Mark Fasheh <mark at fasheh.com>, Joel Becker <jlbec at evilplan.org>
> 
> Looks good.
> Jun, could you please help verify these changes and give your tested-by? Since I don't have ocfs2 cluster locally...
> 
> Thanks,
> Joseph
> 
> On 2020/2/26 14:52, Vasily Averin wrote:
>> v2: resend with improved patch description
>>
>> In Aug 2018 NeilBrown noticed 
>> commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface")
>> "Some ->next functions do not increment *pos when they return NULL...
>> Note that such ->next functions are buggy and should be fixed. 
>> A simple demonstration is
>>    
>> dd if=/proc/swaps bs=1000 skip=1
>>     
>> Choose any block size larger than the size of /proc/swaps.  This will
>> always show the whole last line of /proc/swaps"
>>
>> /proc/swaps output was fixed recently, however there are lot of other
>> affected files and 4 of them are related to ocfs2.
>>
>> Unfortunately I'm not familiar with ocfs2 and cannot verify the patches locally.
>>
>> Usually you can observe following related problems:
>> - read after lseek beyond end of file, described above by NeilBrown
>>  "dd if=<AFFECTED_FILE> bs=1000 skip=1" will incorrectly generate whole last line
>>
>> - read after lseek on into middle of last line will output expected rest of
>>  last line but then repeat whole last line once again. 
>>
>> - If .show() function generates multi-line output following bash script will never finish.
>>
>>  $ q=;while read -r r;do echo "$((++q)) $r";done < AFFECTED_FILE
>>
>> Link: https://urldefense.com/v3/__https://bugzilla.kernel.org/show_bug.cgi?id=206283__;!!GqivPVa7Brio!KCKPYUMw_U1HxUL22F1ZSc3jh5A-b_7ZVR-iw9uPAprEKFstRKwLXaJmpXuqsTjpGIByXQ$ 
>>
>> Vasily Averin (4):
>>   lockres_seq_next should increase position index
>>   ocfs2_dlm_seq_next should increase position index
>>   nst_seq_next should increase position index
>>   sc_seq_next should increase position index
>>
>>  fs/ocfs2/cluster/netdebug.c | 2 ++
>>  fs/ocfs2/dlm/dlmdebug.c     | 1 +
>>  fs/ocfs2/dlmglue.c          | 1 +
>>  3 files changed, 4 insertions(+)
>>
> .
> 
> 
> .
> 