linux-kernel - [PATCH -mm 3/3] ptrace_check_attach: remove unneeded ->signal != NULL check

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Message-ID: <20071121160033.GA1178@tv-sign.ru>
Date:	Wed, 21 Nov 2007 19:00:33 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Roland McGrath <roland@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH -mm 3/3] ptrace_check_attach: remove unneeded ->signal != NULL check

It is not possible to see the PT_PTRACED task without ->signal/sighand under
tasklist_lock, release_task() does ptrace_unlink() first. If the task was
already released before, ptrace_attach() can't succeed and set PT_PTRACED.
Remove this check.

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- PT/kernel/ptrace.c~3_signal	2007-11-21 16:53:39.000000000 +0300
+++ PT/kernel/ptrace.c	2007-11-21 17:20:24.000000000 +0300
@@ -99,9 +99,12 @@ int ptrace_check_attach(struct task_stru
 	 * be changed by us so it's not changing right after this.
 	 */
 	read_lock(&tasklist_lock);
-	if ((child->ptrace & PT_PTRACED) && child->parent == current &&
-	     child->signal != NULL) {
+	if ((child->ptrace & PT_PTRACED) && child->parent == current) {
 		ret = 0;
+		/*
+		 * child->sighand can't be NULL, release_task()
+		 * does ptrace_unlink() before __exit_signal().
+		 */
 		spin_lock_irq(&child->sighand->siglock);
 		if (is_task_stopped(child))
 			__set_task_state(child, TASK_TRACED);

-
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