[PATCH] sigkill priority fix

If SIGKILL does not have priority, we cannot instantly kill task before it
makes some unexpected job.  It can be critical, but we were unable to
reproduce this easily until Heiko Carstens <Heiko.Carstens@de.ibm.com>
reported this problem on LKML.

Signed-Off-By: Kirill Korotaev <dev@sw.ru>
Signed-Off-By: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 8f3debc77c5..b3c24c732c5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -522,7 +522,16 @@ static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
 {
         int sig = 0;
 
-        sig = next_signal(pending, mask);
+        /* SIGKILL must have priority, otherwise it is quite easy
+         * to create an unkillable process, sending sig < SIGKILL
+         * to self */
+        if (unlikely(sigismember(&pending->signal, SIGKILL))) {
+                if (!sigismember(mask, SIGKILL))
+                        sig = SIGKILL;
+        }
+
+        if (likely(!sig))
+                sig = next_signal(pending, mask);
         if (sig) {
                 if (current->notifier) {
                         if (sigismember(current->notifier_mask, sig)) {