Re: [RFC] proc, coredump: add CoreDumping flag to /proc/pid/status

[Roman Gushchin <guro@fb.com>]

Adding Andrew Morton and Oleg Nesterov to cc.

On Thu, Sep 07, 2017 at 12:17:15PM +0100, Roman Gushchin 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
> 
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: kernel-team@fb.com
> Cc: linux-kernel@vger.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
>