From 95a3540da9c81a5987be810e1d9a83640a366bd5 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 2 Apr 2009 16:58:21 -0700
Subject: [PATCH] ptrace_detach: the wrong wakeup breaks the ERESTARTxxx logic

Another ancient bug. Consider this trivial test-case,

	int main(void)
	{
		int pid = fork();

		if (pid) {
			ptrace(PTRACE_ATTACH, pid, NULL, NULL);
			wait(NULL);
			ptrace(PTRACE_DETACH, pid, NULL, NULL);
		} else {
			pause();
			printf("WE HAVE A KERNEL BUG!!!\n");
		}

		return 0;
	}

the child must not "escape" for sys_pause(), but it can and this was seen
in practice.

This is because ptrace_detach does:

	if (!child->exit_state)
		wake_up_process(child);

this wakeup can happen after this child has already restarted sys_pause(),
because it gets another wakeup from ptrace_untrace().

With or without this patch, perhaps sys_pause() needs a fix.  But this
wakeup also breaks the SIGNAL_STOP_STOPPED logic in ptrace_untrace().

Remove this wakeup.  The caller saw this task in TASK_TRACED state, and
unless it was SIGKILL'ed in between __ptrace_unlink()->ptrace_untrace()
should handle this case correctly.  If it was SIGKILL'ed, we don't need to
wakup the dying tracee too.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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