linux-kernel - Re: [RESEND] proc, coredump: add CoreDumping flag to /proc/pid/status

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Date:   Fri, 22 Sep 2017 18:44:12 +0300
From:   Konstantin Khlebnikov <koct9i@...il.com>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Ingo Molnar <mingo@...nel.org>, kernel-team@...com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RESEND] proc, coredump: add CoreDumping flag to /proc/pid/status

On Thu, Sep 21, 2017 at 2:06 AM, Roman Gushchin <guro@...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.

Makes sense.

Maybe print this line only when task actually makes dump?
And probably expose pid of coredump helper.

Add Oleg into CC.

>
> 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
>
> Signed-off-by: Roman Gushchin <guro@...com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: kernel-team@...com
> Cc: linux-kernel@...r.kernel.org
> ---
>  fs/proc/array.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/fs/proc/array.c b/fs/proc/array.c
> index 88c355574aa0..fc4a0aa7f487 100644
> --- a/fs/proc/array.c
> +++ b/fs/proc/array.c
> @@ -369,6 +369,11 @@ static void task_cpus_allowed(struct seq_file *m, struct task_struct *task)
>                    cpumask_pr_args(&task->cpus_allowed));
>  }
>
> +static inline void task_core_dumping(struct seq_file *m, struct mm_struct *mm)
> +{
> +       seq_printf(m, "CoreDumping:\t%d\n", !!mm->core_state);
> +}
> +
>  int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
>                         struct pid *pid, struct task_struct *task)
>  {
> @@ -379,6 +384,7 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
>
>         if (mm) {
>                 task_mem(m, mm);
> +               task_core_dumping(m, mm);
>                 mmput(mm);
>         }
>         task_sig(m, task);
> --
> 2.13.5
>
> --
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