From: Miroslav Benes <mbenes@suse.cz>
To: jpoimboe@redhat.com, jeyu@kernel.org, jikos@kernel.org
Cc: pmladek@suse.com, lpechacek@suse.cz, pavel@ucw.cz,
live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
Oleg Nesterov <oleg@redhat.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>,
linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks
Date: Wed, 1 Nov 2017 16:06:19 +0100 (CET) [thread overview]
Message-ID: <alpine.LSU.2.21.1711011602370.7846@san.suse.cz> (raw)
In-Reply-To: <20171031114853.841-2-mbenes@suse.cz>
> +/*
> + * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
> + * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this
> + * action currently.
> + */
> +void klp_force_signals(void)
> +{
> + struct task_struct *g, *task;
> +
> + pr_notice("signaling remaining tasks\n");
> +
> + read_lock(&tasklist_lock);
> + for_each_process_thread(g, task) {
> + if (!klp_patch_pending(task))
> + continue;
> +
> + /*
> + * There is a small race here. We could see TIF_PATCH_PENDING
> + * set and decide to wake up a kthread or send a fake signal.
> + * Meanwhile the task could migrate itself and the action
> + * would be meaningless. It is not serious though.
> + */
> + if (task->flags & PF_KTHREAD) {
> + /*
> + * Wake up a kthread which still has not been migrated.
> + */
> + wake_up_process(task);
So this is not as safe as one would hope. It tries to wake all TASK_NORMAL
tasks, which could cause headaches. Let's make it
wake_up_state(task, TASK_INTERRUPTIBLE);
to wake only kthreads sleeping interruptedly.
Thanks Petr for spotting this (offline).
Miroslav
> + } else {
> + /*
> + * Send fake signal to all non-kthread tasks which are
> + * still not migrated.
> + */
> + spin_lock_irq(&task->sighand->siglock);
> + signal_wake_up(task, 0);
> + spin_unlock_irq(&task->sighand->siglock);
> + }
> + }
> + read_unlock(&tasklist_lock);
> +}
next prev parent reply other threads:[~2017-11-01 15:06 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-31 11:48 [PATCH v3 0/2] livepatch: Introduce signal and force sysfs attributes Miroslav Benes
2017-10-31 11:48 ` [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks Miroslav Benes
2017-11-01 15:06 ` Miroslav Benes [this message]
2017-11-01 15:13 ` Petr Mladek
2017-11-01 16:43 ` Oleg Nesterov
2017-11-02 10:36 ` Miroslav Benes
2017-11-02 14:08 ` Oleg Nesterov
2017-11-02 13:09 ` Josh Poimboeuf
2017-11-03 8:02 ` Miroslav Benes
2017-11-03 12:57 ` Josh Poimboeuf
2017-11-02 13:32 ` Josh Poimboeuf
2017-11-03 8:06 ` Miroslav Benes
2017-11-06 11:08 ` Pavel Machek
2017-10-31 11:48 ` [PATCH v3 2/2] livepatch: force transition process to finish Miroslav Benes
2017-11-01 15:32 ` Petr Mladek
2017-11-02 13:13 ` Josh Poimboeuf
2017-11-03 8:07 ` Miroslav Benes
2017-11-06 11:11 ` Pavel Machek
2017-11-06 12:03 ` Jiri Kosina
2017-11-09 11:14 ` Pavel Machek
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