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Commit 64a4096c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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ptrace: ptrace_detach() can no longer race with SIGKILL 



ptrace_detach() re-checks ->ptrace under tasklist lock and calls
release_task() if __ptrace_detach() returns true.  This was needed because
the __TASK_TRACED tracee could be killed/untraced, and it could even pass
exit_notify() before we take tasklist_lock.

But this is no longer possible after 9899d11f "ptrace: ensure
arch_ptrace/ptrace_request can never race with SIGKILL".  We can turn
these checks into WARN_ON() and remove release_task().

While at it, document the setting of child->exit_code.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Pavel Labath <labath@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b72c1869

kernel/ptrace.c

+9 −10
Original line number Diff line number Diff line
@@ -456,8 +456,6 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p) 


static int ptrace_detach(struct task_struct *child, unsigned int data)

{

	bool dead = false;



	if (!valid_signal(data))

		return -EIO;
@@ -467,18 +465,19 @@ static int ptrace_detach(struct task_struct *child, unsigned int data) 


	write_lock_irq(&tasklist_lock);

	/*

	 * This child can be already killed. Make sure de_thread() or

	 * our sub-thread doing do_wait() didn't do release_task() yet.

	 * We rely on ptrace_freeze_traced(). It can't be killed and

	 * untraced by another thread, it can't be a zombie.

	 */

	WARN_ON(!child->ptrace || child->exit_state);

	/*

	 * tasklist_lock avoids the race with wait_task_stopped(), see

	 * the comment in ptrace_resume().

	 */

	if (child->ptrace) {

	child->exit_code = data;

		dead = __ptrace_detach(current, child);

	}

	__ptrace_detach(current, child);

	write_unlock_irq(&tasklist_lock);



	proc_ptrace_connector(child, PTRACE_DETACH);

	if (unlikely(dead))

		release_task(child);



	return 0;

}