Use write_trylock_irqsave in ptrace_attach

This patch makes ptrace_attach use write_trylock_irqsave().

[akpm@linux-foundation.org: remove unneeded initialisation]
Signed-off-by: Sripathi Kodi <sripathik@in.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/ptrace.c

@@ -161,6 +161,7 @@ int ptrace_may_attach(struct task_struct *task)
 int ptrace_attach(struct task_struct *task)
 {
 	int retval;
+	unsigned long flags;
 
 	audit_ptrace(task);
 
@@ -181,9 +182,7 @@ repeat:
 	 * cpu's that may have task_lock).
 	 */
 	task_lock(task);
-	local_irq_disable();
+	if (!write_trylock_irqsave(&tasklist_lock, flags)) {
-	if (!write_trylock(&tasklist_lock)) {
-		local_irq_enable();
 		task_unlock(task);
 		do {
 			cpu_relax();
@@ -211,7 +210,7 @@ repeat:
 	force_sig_specific(SIGSTOP, task);
 
 bad:
-	write_unlock_irq(&tasklist_lock);
+	write_unlock_irqrestore(&tasklist_lock, flags);
 	task_unlock(task);
 out:
 	return retval;