From 6405f7f4675884b671bee66678e1c2859bdb0e56 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@tv-sign.ru>
Date: Fri, 8 Feb 2008 04:19:00 -0800
Subject: [PATCH] ptrace_stop: fix the race with ptrace detach+attach

If the tracer went away (may_ptrace_stop() failed), ptrace_stop() drops
tasklist and then changes the ->state from TASK_TRACED to TASK_RUNNING.

This can fool another tracer which attaches to us in between.  Change the
->state under tasklist_lock to ensure that ptrace_check_attach() can't wrongly
succeed.  Also, remove the unnecessary mb().

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