linux-kernel - [PATCH 3.10 105/319] coredump: fix unfreezable coredumping task

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Date:   Sun,  5 Feb 2017 20:18:47 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 105/319] coredump: fix unfreezable coredumping task

From: Andrey Ryabinin <aryabinin@...tuozzo.com>

commit 70d78fe7c8b640b5acfad56ad341985b3810998a upstream.

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'.

Inability to freeze a task during suspend will cause suspend to fail.
Also CRIU uses cgroup freezer during dump operation.  So with an
unfreezable task the CRIU dump will fail because it waits for a
transition from 'FREEZING' to 'FROZEN' state which will never happen.

Use freezer_do_not_count() to tell freezer to ignore coredumping task
while it waits for core_state->startup completion.

Link: http://lkml.kernel.org/r/1475225434-3753-1-git-send-email-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
Acked-by: Pavel Machek <pavel@....cz>
Acked-by: Oleg Nesterov <oleg@...hat.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Tejun Heo <tj@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Michal Hocko <mhocko@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 fs/coredump.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/coredump.c b/fs/coredump.c
index 4f03b2b..a94f94d 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>
@@ -375,7 +376,9 @@ 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
-- 
2.8.0.rc2.1.gbe9624a