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Message-ID: <alpine.DEB.2.20.1712200943570.4025@hypnos.tec.linutronix.de> Date: Wed, 20 Dec 2017 09:44:34 +0100 (CET) From: Anna-Maria Gleixner <anna-maria@...utronix.de> To: Peter Zijlstra <peterz@...radead.org> cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>, Christoph Hellwig <hch@....org>, keescook@...omium.org, John Stultz <john.stultz@...aro.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH 17/25] hrtimer: Implementation of softirq hrtimer handling On Tue, 19 Dec 2017, Peter Zijlstra wrote: > On Tue, Dec 19, 2017 at 09:58:44AM +0100, Sebastian Andrzej Siewior wrote: > > this is late I know… > > > > On 2017-09-27 18:40:26 [+0200], Peter Zijlstra wrote: > > > - removed superfluous local_bh_disable(), since local_irq_disable() > > > already implies much the same. > > > > it is not superfluous. > > > > > Please consider... > > > > > > @@ -1768,7 +1786,6 @@ int hrtimers_dead_cpu(unsigned int scpu) > > > BUG_ON(cpu_online(scpu)); > > > tick_cancel_sched_timer(scpu); > > > > > > - local_bh_disable(); > > > local_irq_disable(); > > > old_base = &per_cpu(hrtimer_bases, scpu); > > > new_base = this_cpu_ptr(&hrtimer_bases); > > > @@ -1796,7 +1813,6 @@ int hrtimers_dead_cpu(unsigned int scpu) > > > /* Check, if we got expired work to do */ > > > __hrtimer_peek_ahead_timers(); > > > local_irq_enable(); > > > - local_bh_enable(); > > > return 0; > > > } > > > > we need in there. That local_bh_disable() is required in order to let > > raise_softirq_irqoff() not do anything stupid in particular we need > > !in_interrupt() defer wakeup_softirqd() until local_bh_enable(). > > Otherwise wakeup_softirqd() might actually try to wakeup the process and > > go after the pi_lock which can't happen while holding cpu_base->lock. > > Argh, that's horrible and definitely needs a comment. > will add it in v4 with a comment. Anna-Maria
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