linux-kernel - Re: [PATCHv2] printk: queue wake_up_klogd irq

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Message-ID: <20200410030704.GA20227@jagdpanzerIV.localdomain>
Date:   Fri, 10 Apr 2020 12:07:04 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Simon Kirby <sim@...tway.ca>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Lech Perczak <l.perczak@...lintechnologies.com>,
        Theodore Ts'o <tytso@....edu>,
        John Ogness <john.ogness@...utronix.de>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCHv2] printk: queue wake_up_klogd irq_work only if per-CPU
 areas are ready

On (20/04/09 12:25), Simon Kirby wrote:
> This causes "dmesg -w" or "cat /dev/kmsg" to not print new messages after
> dumping the current ring. I hit this on v5.5.9, v5.5.15, v5.6.3, and
> Linus HEAD. This prints no "hi":
> 
> (sleep 1;echo hi > /dev/kmsg)& dmesg -w
> 
> ...curiously, "strace dmesg -w" shows the data received once ^C is hit.
> 
> Jann pointed me to this patch. Applying it or reverting 1b710b1b10eff9d4
> does fix it for me. However, Linus HEAD is still broken and, AFAICS,
> remains unreverted and unfixed in stable/linux-5.4.y through linux-5.6.y.
> It was introduced in 5.6 but backported to those, not just the LTS above.

I'm trying to land this patch. Give me a moment, I'll come back to
you shortly.

	-ss