signals: move cred_guard_mutex from task_struct to signal_struct

Oleg Nesterov pointed out we have to prevent multiple-threads-inside-exec
itself and we can reuse ->cred_guard_mutex for it.  Yes, concurrent
execve() has no worth.

Let's move ->cred_guard_mutex from task_struct to signal_struct.  It
naturally prevent multiple-threads-inside-exec.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 2fea6c8ef6ba..1f8c06ce0fa6 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -29,6 +29,8 @@ extern struct fs_struct init_fs;
                 .running = 0,                                           \
                 .lock = __SPIN_LOCK_UNLOCKED(sig.cputimer.lock),        \
         },                                                              \
+        .cred_guard_mutex =                                             \
+                 __MUTEX_INITIALIZER(sig.cred_guard_mutex),             \
 }
 
 extern struct nsproxy init_nsproxy;
@@ -145,8 +147,6 @@ extern struct cred init_cred;
         .group_leader   = &tsk,                                         \
         RCU_INIT_POINTER(.real_cred, &init_cred),                       \
         RCU_INIT_POINTER(.cred, &init_cred),                            \
-        .cred_guard_mutex =                                             \
-                 __MUTEX_INITIALIZER(tsk.cred_guard_mutex),             \
         .comm           = "swapper",                                    \
         .thread         = INIT_THREAD,                                  \
         .fs             = &init_fs,                                     \