linux-kernel - Re: [PATCH] zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF

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Date: Thu, 13 Jun 2024 16:49:13 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Wei Fu <fuweid89@...il.com>
Cc: ebiederm@...ssion.com, Sudhanva.Huruli@...rosoft.com,
	akpm@...ux-foundation.org, apais@...ux.microsoft.com,
	axboe@...nel.dk, boqun.feng@...il.com, brauner@...nel.org,
	frederic@...nel.org, j.granados@...sung.com, jiangshanlai@...il.com,
	joel@...lfernandes.org, josh@...htriplett.org,
	linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
	michael.christie@...cle.com, mjguzik@...il.com,
	neeraj.upadhyay@...nel.org, paulmck@...nel.org,
	qiang.zhang1211@...il.com, rachelmenge@...ux.microsoft.com,
	rcu@...r.kernel.org, rostedt@...dmis.org
Subject: Re: [PATCH] zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with
 TIF_SIGPENDING

On 06/13, Wei Fu wrote:
>
> I think there is a case that TIF_NOTIFY_SIGNAL remains set.

[...snip...]

Of course! but please forget about io_uring even if currently io_uring/
is the only user of TWA_SIGNAL.

Just suppose that the exiting task/thread races with task_workd_add(TWA_SIGNAL),
TIF_NOTIFY_SIGNAL won't be cleared.

This is fine in that the exiting task T will do exit_task_work() and after that
task_work_add(T) can't succeed with or without TWA_SIGNAL. So it can't miss the
pending work.

But I think we can forget about TIF_NOTIFY_SIGNAL. To me, the problem is that
the state of signal_pending() of the exiting task was never clearly defined, and
I can't even recall how many times I mentioned this in the previous discussions.
TIF_NOTIFY_SIGNAL doesn't add more confusion, imo.

Oleg.