[Devel] [PATCH] pid_ns: Sleep in TASK_INTERRUPTIBLE in zap_pid_ns_processes

[Kirill Tkhai]

This patch by Eric W. Biederman will go to 4.12-rc2:
https://www.spinics.net/lists/linux-containers/msg32521.html

The code can potentially sleep for an indefinite amount of time in
zap_pid_ns_processes triggering the hung task timeout, and increasing
the system average.  This is undesirable.  Sleep with a task state of
TASK_INTERRUPTIBLE instead of TASK_UNINTERRUPTIBLE to remove these
undesirable side effects.

Apparently under heavy load this has been allowing Chrome to trigger
the hung time task timeout error and cause ChromeOS to reboot.

Reported-by: Vovo Yang <vovoy at google.com>
Reported-by: Guenter Roeck <linux at roeck-us.net>
Tested-by: Guenter Roeck <linux at roeck-us.net>
Fixes: 6347e9009104 ("pidns: guarantee that the pidns init will be the last pidns process reaped")
Cc: stable at vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
---
 kernel/pid_namespace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 594167d9693..028e864523a 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -241,7 +241,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 	 * Make sure they all go away, see free_pid().
 	 */
 	for (;;) {
-		set_current_state(TASK_UNINTERRUPTIBLE);
+		set_current_state(TASK_INTERRUPTIBLE);
 		if (pid_ns->nr_hashed == init_pids)
 			break;
 		schedule();