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Tue, 04 Feb 2025 06:23:08 -0500 X-MC-Unique: 0OEyAW2xOFSETkgQLcfn0A-1 X-Mimecast-MFC-AGG-ID: 0OEyAW2xOFSETkgQLcfn0A Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1E697195608A; Tue, 4 Feb 2025 11:23:07 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.72]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 816531800268; Tue, 4 Feb 2025 11:23:04 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 4 Feb 2025 12:22:41 +0100 (CET) Date: Tue, 4 Feb 2025 12:22:37 +0100 From: Oleg Nesterov To: Mateusz Guzik Cc: ebiederm@xmission.com, brauner@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 3/6] exit: postpone tty_kref_put() until after tasklist_lock is dropped Message-ID: <20250204112236.GA6031@redhat.com> References: <20250201163106.28912-1-mjguzik@gmail.com> <20250201163106.28912-4-mjguzik@gmail.com> <20250203180623.GC1003@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Stat-Signature: u5s8cw5oeg8wcmfbs4w6cd7gwtrx5pis X-Rspam-User: X-Rspamd-Queue-Id: 12043C0003 X-Rspamd-Server: rspam03 X-HE-Tag: 1738668194-458833 X-HE-Meta: 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 Oz3h35bW y1EwBU+NkW5aE261X8sabx2ccw8mviiEILMEdCj5ZD9rB7MPnJGXg4WLYTaChL5gWh5rb2FyPMttUShj93Uzq8LHR9UY/cPpgH8toobue4C81dAtCrZ6TcmYTDtTG4njJPnw6IbKFGzRqQ0MrZn066yrN/gmIS82huNXYnqhcquK0KiVp/xxGMXAznGbBWKreMi0AL6rZbMt1PUFK+NNC/uYvkWCVrqO0YU9StwhSeZgdCI5qJzG+92Zm+6H6GOy/AVevpL93GLcrpOz4q6a+nFhuEG9bT64W1i25tZhY+gRZw3DyDHtW0N/c+spwe0f9NQg9AXb4LI6BGyu6LooG6i38ERb+LXJhp1FD52u8NqDBOz7GbNPo4ZzHbYmzH3Zq7DN0AT4aq+0r1oXyfln7BdUOTw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 02/03, Mateusz Guzik wrote: > > On Mon, Feb 3, 2025 at 7:07 PM Oleg Nesterov wrote: > > > > On 02/01, Mateusz Guzik wrote: > > > > > > Instead of smuggling the tty pointer directly, use a struct so that more > > > things can be added later. > > > > I am not sure this particular change worth the effort, but I won't argue. > > I'd like to know what Eric thinks. > > > > it trivially whacks an atomic from an area protected by a global lock Yes, but I am not sure this can make a noticeable difference... Let me repeat, I am not really arguing, I leave this to you and Eric. The patch looks correct and I have already acked it. Just it looks "less obvious" to me than other changes in this series. And even if we do this, I am not sure we need the new "struct release_task_post", it seems we can simply move tty_kref_put() from __exit_signal() to release_task(), see the patch at the end. Nobody can touch signal->tty after the group leader passes __exit_signal(), if nothing else lock_task_sighand() can't succeed. But again, feel free to ignore. Oleg. --- x/kernel/exit.c +++ x/kernel/exit.c @@ -146,7 +146,6 @@ static void __exit_signal(struct task_st struct signal_struct *sig = tsk->signal; bool group_dead = thread_group_leader(tsk); struct sighand_struct *sighand; - struct tty_struct *tty; u64 utime, stime; sighand = rcu_dereference_check(tsk->sighand, @@ -159,10 +158,7 @@ static void __exit_signal(struct task_st posix_cpu_timers_exit_group(tsk); #endif - if (group_dead) { - tty = sig->tty; - sig->tty = NULL; - } else { + if (!group_dead) { /* * If there is any task waiting for the group exit * then notify it: @@ -210,10 +206,8 @@ static void __exit_signal(struct task_st __cleanup_sighand(sighand); clear_tsk_thread_flag(tsk, TIF_SIGPENDING); - if (group_dead) { + if (group_dead) flush_sigqueue(&sig->shared_pending); - tty_kref_put(tty); - } } static void delayed_put_task_struct(struct rcu_head *rhp) @@ -279,6 +273,10 @@ repeat: proc_flush_pid(thread_pid); put_pid(thread_pid); release_thread(p); + + if (p == leader) + tty_kref_put(p->signal->tty); + put_task_struct_rcu_user(p); p = leader;