commit 87245135d5057edd5a8037131f81eeffd76d4fef
author Oleg Nesterov <oleg@redhat.com> Wed Jun 17 16:27:23 2009 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Thu Jun 18 13:03:48 2009 -0700
tree 9c6c695f474dfced54311467fd5c14de57f6dbb9
parent 2ffebca6aa7e1687905c842dd8c5c1e811e574e7

allow_signal: kill the bogus ->mm check, add a note about CLONE_SIGHAND

allow_signal() checks ->mm == NULL.  Not sure why.  Perhaps to make sure
current is the kernel thread.  But this helper must not be used unless we
are the kernel thread, kill this check.

Also, document the fact that the CLONE_SIGHAND kthread must not use
allow_signal(), unless the caller really wants to change the parent's
->sighand->action as well.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

diff --git a/kernel/exit.c b/kernel/exit.c
index b6c90b5..533e5f8 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -375,9 +375,8 @@
 }
 
 /*
- * Let kernel threads use this to say that they
- * allow a certain signal (since daemonize() will
- * have disabled all of them by default).
+ * Let kernel threads use this to say that they allow a certain signal.
+ * Must not be used if kthread was cloned with CLONE_SIGHAND.
  */
 int allow_signal(int sig)
 {
@@ -385,14 +384,14 @@
 		return -EINVAL;
 
 	spin_lock_irq(&current->sighand->siglock);
+	/* This is only needed for daemonize()'ed kthreads */
 	sigdelset(&current->blocked, sig);
-	if (!current->mm) {
-		/* Kernel threads handle their own signals.
-		   Let the signal code know it'll be handled, so
-		   that they don't get converted to SIGKILL or
-		   just silently dropped */
-		current->sighand->action[(sig)-1].sa.sa_handler = (void __user *)2;
-	}
+	/*
+	 * Kernel threads handle their own signals. Let the signal code
+	 * know it'll be handled, so that they don't get converted to
+	 * SIGKILL or just silently dropped.
+	 */
+	current->sighand->action[(sig)-1].sa.sa_handler = (void __user *)2;
 	recalc_sigpending();
 	spin_unlock_irq(&current->sighand->siglock);
 	return 0;