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

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

[Roman Gushchin]

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

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

[Roman Gushchin]

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.
> 

Ping?

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

[Alexey Dobriyan]

> 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.

Or add "State: C" ?

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

[Roman Gushchin]

On Thu, Sep 14, 2017 at 01:15:26AM +0300, Alexey Dobriyan wrote:
> > 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.
> 
> Or add "State: C" ?

A program in such state can also sleep and run, so it's not
a state in terms of process states.

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

[Alexey Dobriyan]

On Wed, Sep 13, 2017 at 03:21:59PM -0700, Roman Gushchin wrote:
> On Thu, Sep 14, 2017 at 01:15:26AM +0300, Alexey Dobriyan wrote:
> > > 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.
> > 
> > Or add "State: C" ?
> 
> A program in such state can also sleep and run, so it's not
> a state in terms of process states.

Well, maybe something will break from seeing unknown process state.

Regardless, symlink /proc/$PID/coredump pointing to either "0" or "1"
is faster than open+read+parse+close.

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

[Roman Gushchin]

On Thu, Sep 14, 2017 at 01:46:43AM +0300, Alexey Dobriyan wrote:
> On Wed, Sep 13, 2017 at 03:21:59PM -0700, Roman Gushchin wrote:
> > On Thu, Sep 14, 2017 at 01:15:26AM +0300, Alexey Dobriyan wrote:
> > > > 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.
> > > 
> > > Or add "State: C" ?
> > 
> > A program in such state can also sleep and run, so it's not
> > a state in terms of process states.
> 
> Well, maybe something will break from seeing unknown process state.
> 
> Regardless, symlink /proc/$PID/coredump pointing to either "0" or "1"
> is faster than open+read+parse+close.

Performance doesn't really matter in this case: nobody should check
this flag often. An expected usecase is described above: check the flag
once before killing the process by timeout.
So, it doesn't look deserving a separate entity in procfs.

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

[Roman Gushchin]

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
>