linux-kernel - Re: [printk] 18a2dc6982: ltp.kmsg01.fail

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Date:   Thu, 9 Jul 2020 17:33:23 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     kernel test robot <rong.a.chen@...el.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul McKenney <paulmck@...nel.org>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, lkp@...ts.01.org
Subject: Re: [printk] 18a2dc6982: ltp.kmsg01.fail

On (20/07/09 15:14), kernel test robot wrote:
[..]

Took me a while to find the FAIL-ed test:

> kmsg01.c:393: INFO: TEST: read returns EPIPE when messages get overwritten
> kmsg01.c:398: INFO: first seqno: 0
> kmsg01.c:411: INFO: first seqno now: 881
> kmsg01.c:425: FAIL: read returned: 77: SUCCESS (0)

So this is seq number related
https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/logging/kmsg/kmsg01.c#L383

LTP writes a gazillion (roughly, maybe a bit less than that)
filler messages to /dev/kmsg in order to cause logbuf overlap:
...
19490 [  172.301584] LTP kmsg01 FILLER MESSAGE TO OVERWRITE OTHERS
19491 [  172.308730] LTP kmsg01 FILLER MESSAGE TO OVERWRITE OTHERS
19492 [  172.313852] LTP kmsg01 FILLER MESSAGE TO OVERWRITE OTHERS
19493 [  172.320988] LTP kmsg01 FILLER MESSAGE TO OVERWRITE OTHERS
19494 [  172.325618] LTP kmsg01 FILLER MESSAGE TO OVERWRITE OTHERS
...

	-ss