[Devel] [PATCH RHEL7 COMMIT] ms/coredump: fix unfreezable coredumping task

[Kirill Tkhai]

The commit is pushed to "branch-rh7-3.10.0-327.36.1.vz7.18.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.36.1.vz7.18.3
------>
commit 6626da2a1f42e5c5abeb258904fd1db494df4629
Author: Andrey Ryabinin <aryabinin at virtuozzo.com>
Date:   Mon Oct 3 14:56:10 2016 +0000

    ms/coredump: fix unfreezable coredumping task
    
    It could be not possible to freeze coredumping task when it waits
    for 'core_state->startup' completion, because threads are frozen
    in get_signal() before they got a chance to complete 'core_state->startup'.
    
    Use freezer_do_not_count() to tell freezer to ignore coredumping
    task while it waits for core_state->startup completion.
    
    https://jira.sw.ru/browse/PSBM-52793
    
    Link: http://lkml.kernel.org/r/1475225434-3753-1-git-send-email-aryabinin@virtuozzo.com
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
    
    Cc: stable at vger.kernel.org
    Acked-by: Oleg Nesterov <oleg at redhat.com>
    Acked-by: Pavel Machek <pavel at ucw.cz>
    Reviewed-by: Dmitry Safonov <dsafonov at virtuozzo.com>
---
 fs/coredump.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/coredump.c b/fs/coredump.c
index e3fdee2..f6a1012 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -1,6 +1,7 @@
 #include <linux/slab.h>
 #include <linux/file.h>
 #include <linux/fdtable.h>
+#include <linux/freezer.h>
 #include <linux/mm.h>
 #include <linux/stat.h>
 #include <linux/fcntl.h>
@@ -388,7 +389,9 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
 	if (core_waiters > 0) {
 		struct core_thread *ptr;
 
+		freezer_do_not_count();
 		wait_for_completion(&core_state->startup);
+		freezer_count();
 		/*
 		 * Wait for all the threads to become inactive, so that
 		 * all the thread context (extended register state, like