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Date: Wed, 1 Nov 2017 16:06:19 +0100 (CET) From: Miroslav Benes <mbenes@...e.cz> To: jpoimboe@...hat.com, jeyu@...nel.org, jikos@...nel.org cc: pmladek@...e.com, lpechacek@...e.cz, pavel@....cz, live-patching@...r.kernel.org, linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>, Michael Ellerman <mpe@...erman.id.au>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, linuxppc-dev@...ts.ozlabs.org, x86@...nel.org Subject: Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks > +/* > + * 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); > +}
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