Received-SPF: pass (google.com: domain of linux-kernel+bounces-213469-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Thu, 13 Jun 2024 16:49:13 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Wei Fu <fuweid89@gmail.com>
Cc: ebiederm@xmission.com, Sudhanva.Huruli@microsoft.com,
	akpm@linux-foundation.org, apais@linux.microsoft.com,
	axboe@kernel.dk, boqun.feng@gmail.com, brauner@kernel.org,
	frederic@kernel.org, j.granados@samsung.com, jiangshanlai@gmail.com,
	joel@joelfernandes.org, josh@joshtriplett.org,
	linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com,
	michael.christie@oracle.com, mjguzik@gmail.com,
	neeraj.upadhyay@kernel.org, paulmck@kernel.org,
	qiang.zhang1211@gmail.com, rachelmenge@linux.microsoft.com,
	rcu@vger.kernel.org, rostedt@goodmis.org
Subject: Re: [PATCH] zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with
 TIF_SIGPENDING
Message-ID: <20240613144913.GA18218@redhat.com>
References: <87a5jpqamx.fsf@email.froward.int.ebiederm.org>
 <20240613140216.30327-1-fuweid89@gmail.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240613140216.30327-1-fuweid89@gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)

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.