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, 1 insertions, 1 deletions

diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 10db0102a890..3a2e66d88a32 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -150,7 +150,7 @@ static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
  *
  * Return %LSM_UNSAFE_* bits applied to an exec because of tracing.
  *
- * @task->cred_guard_mutex is held by the caller through the do_execve().
+ * @task->signal->cred_guard_mutex is held by the caller through the do_execve().
  */
 static inline int tracehook_unsafe_exec(struct task_struct *task)
 {