Re: [PATCH v2 2/5] sched,ptrace: Fix ptrace_check_attach() vs PREEMPT_RT

[Peter Zijlstra]

On Tue, Apr 26, 2022 at 07:24:03PM -0500, Eric W. Biederman wrote:
> But doing:
> 
> 	/* Don't stop if the task is dying */
> 	if (unlikely(__fatal_signal_pending(current)))
> 		return exit_code;
> 
> Should work.

Something like so then...

---
Subject: signal,ptrace: Don't stop dying tasks
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu Apr 28 22:17:56 CEST 2022

Oleg pointed out that the tracee can already be killed such that
fatal_signal_pending() is true. In that case signal_wake_up_state()
cannot be relied upon to be responsible for the wakeup -- something
we're going to want to rely on.

As such, explicitly handle this case.

Suggested-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/signal.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2226,6 +2226,10 @@ static int ptrace_stop(int exit_code, in
 		spin_lock_irq(&current->sighand->siglock);
 	}
 
+	/* Don't stop if the task is dying. */
+	if (unlikely(__fatal_signal_pending(current)))
+		return exit_code;
+
 	/*
 	 * schedule() will not sleep if there is a pending signal that
 	 * can awaken the task.