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

[Roman Gushchin <guro@fb.com>]

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: Andrew Morton <akpm@linux-foundation.org>
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

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