From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Qian Cai <cai@lca.pw>,
akpm@linux-foundation.org, bigeasy@linutronix.de,
tglx@linutronix.de, thgarnie@google.com, tytso@mit.edu,
cl@linux.com, penberg@kernel.org, rientjes@google.com,
mingo@redhat.com, will@kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, keescook@chromium.org
Subject: Re: [PATCH] sched: Avoid spurious lock dependencies
Date: Tue, 1 Oct 2019 15:44:10 +0200 [thread overview]
Message-ID: <20191001134410.GL4536@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191001113513.GB32306@linux.vnet.ibm.com>
On Tue, Oct 01, 2019 at 05:06:56PM +0530, Srikar Dronamraju wrote:
> > Subject: sched: Avoid spurious lock dependencies
> >
> > While seemingly harmless, __sched_fork() does hrtimer_init(), which,
> > when DEBUG_OBJETS, can end up doing allocations.
> >
>
> NIT: s/DEBUG_OBJETS/DEBUG_OBJECTS
>
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 7880f4f64d0e..1832fc0fbec5 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -6039,10 +6039,11 @@ void init_idle(struct task_struct *idle, int cpu)
> > struct rq *rq = cpu_rq(cpu);
> > unsigned long flags;
> >
> > + __sched_fork(0, idle);
> > +
> > raw_spin_lock_irqsave(&idle->pi_lock, flags);
> > raw_spin_lock(&rq->lock);
> >
> > - __sched_fork(0, idle);
> > idle->state = TASK_RUNNING;
> > idle->se.exec_start = sched_clock();
> > idle->flags |= PF_IDLE;
> >
>
> Given that there is a comment just after this which says
> "init_task() gets called multiple times on a task",
> should we add a check if rq->idle is present and bail out?
>
> if (rq->idle) {
> raw_spin_unlock(&rq->lock);
> raw_spin_unlock_irqrestore(&idle->pi_lock, flags);
> return;
> }
Not really worth it; the best solution is to fix the callchains leading
up to it. It's all hotplug related IIRC and so it's slow anyway.
> Also can we also move the above 3 statements before the lock?
Probably, but to what effect?
next prev parent reply other threads:[~2019-10-01 13:44 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-13 16:27 [PATCH] mm/slub: fix a deadlock in shuffle_freelist() Qian Cai
2019-09-16 9:03 ` Sebastian Andrzej Siewior
2019-09-16 14:01 ` Qian Cai
2019-09-16 19:51 ` Sebastian Andrzej Siewior
2019-09-16 21:31 ` Qian Cai
2019-09-17 7:16 ` Sebastian Andrzej Siewior
2019-09-18 19:59 ` Qian Cai
2019-09-25 9:31 ` Peter Zijlstra
2019-09-25 15:18 ` Qian Cai
2019-09-25 16:45 ` Peter Zijlstra
2019-09-26 12:29 ` Qian Cai
2019-10-01 9:18 ` [PATCH] sched: Avoid spurious lock dependencies Peter Zijlstra
2019-10-01 10:01 ` Valentin Schneider
2019-10-01 11:22 ` Qian Cai
2019-10-01 11:36 ` Srikar Dronamraju
2019-10-01 13:44 ` Peter Zijlstra [this message]
2019-10-29 11:10 ` Qian Cai
2019-10-29 12:44 ` Peter Zijlstra
2019-11-12 0:54 ` Qian Cai
2019-11-13 10:06 ` [tip: sched/urgent] sched/core: " tip-bot2 for Peter Zijlstra
2019-11-22 20:01 ` Sebastian Andrzej Siewior
2019-11-22 20:20 ` Peter Zijlstra
2019-11-22 21:03 ` Qian Cai
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