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Date: Wed, 27 Sep 2017 16:31:06 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Roman Gushchin <guro@fb.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, <linux-mm@kvack.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Ingo Molnar <mingo@kernel.org>, <kernel-team@fb.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [RESEND] proc, coredump: add CoreDumping flag to
 /proc/pid/status
Message-Id: <20170927163106.84b9622f183f087eff7f6da7@linux-foundation.org>
In-Reply-To: <20170920230634.31572-1-guro@fb.com>
References: <20170914224431.GA9735@castle>
        <20170920230634.31572-1-guro@fb.com>
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On Wed, 20 Sep 2017 16:06:34 -0700 Roman Gushchin <guro@fb.com> wrote:

> Right now there is no convenient way to check if a process is being
> coredumped at the moment.
> 
> It might be necessary to recognize such state to prevent killing
> the process and getting a broken coredump.
> Writing a large core might take significant time, and the process
> is unresponsive during it, so it might be killed by timeout,
> if another process is monitoring and killing/restarting
> hanging tasks.
> 
> To provide an ability to detect if a process is in the state of
> being coreduped, we can expose a boolean CoreDumping flag
> in /proc/pid/status.
> 
> Example:
> $ cat core.sh
>   #!/bin/sh
> 
>   echo "|/usr/bin/sleep 10" > /proc/sys/kernel/core_pattern
>   sleep 1000 &
>   PID=$!
> 
>   cat /proc/$PID/status | grep CoreDumping
>   kill -ABRT $PID
>   sleep 1
>   cat /proc/$PID/status | grep CoreDumping
> 
> $ ./core.sh
>   CoreDumping:	0
>   CoreDumping:	1

I assume you have some real-world use case which benefits from this.

>  fs/proc/array.c | 6 ++++++
>  1 file changed, 6 insertions(+)

A Documentation/ would be appropriate?   Include a brief mention of
*why* someone might want to use this...