oom: kill all threads that share mm with killed task

oom_kill_task() calls __oom_kill_task() to OOM kill a selected task.
When finding other threads that share an mm with that task, we need to
kill those individual threads and not the same one.

(Bug introduced by f2a2a710)
Acked-by: William Irwin <bill.irwin@oracle.com>
Acked-by: Christoph Lameter <clameter@engr.sgi.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -333,7 +333,7 @@ static int oom_kill_task(struct task_struct *p)
 	 */
 	do_each_thread(g, q) {
 		if (q->mm == mm && q->tgid != p->tgid)
-			force_sig(SIGKILL, p);
+			force_sig(SIGKILL, q);
 	} while_each_thread(g, q);
 
 	return 0;