coredump: fix unfreezable coredumping task

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@virtuozzo.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Tejun Heo <tj@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/exec.c b/fs/exec.c
index a0006d8..3f8d8f3 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -25,6 +25,7 @@
 #include <linux/slab.h>
 #include <linux/file.h>
 #include <linux/fdtable.h>
 #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>
 #include <linux/mm.h>
 #include <linux/stat.h>
 #include <linux/fcntl.h>


@@ -1974,8 +1975,11 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
                complete(vfork_done);
        }
 
                complete(vfork_done);
        }
 

-       if (core_waiters)
+       if (core_waiters > 0) {
+               freezer_do_not_count();

                wait_for_completion(&core_state->startup);
                wait_for_completion(&core_state->startup);

+               freezer_count();
+       }

 fail:
        return core_waiters;
 }
 fail:
        return core_waiters;
 }