linux-kernel - Re: Do we need to disable preemption in flush_tlb

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Message-ID: <20180315082720.GT4064@hirez.programming.kicks-ass.net>
Date:   Thu, 15 Mar 2018 09:27:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
Subject: Re: Do we need to disable preemption in flush_tlb_range()?

On Wed, Mar 14, 2018 at 01:19:01PM -0700, Vineet Gupta wrote:
> +CC Peter since we have his attention ;-)

Yeah, timezone collision there, I typically sleep at 1am ;-)

> On 03/01/2018 07:13 AM, Alexey Brodkin wrote:
> > Hi Vineet,
> > 
> > Just noticed that in comments for smp_call_function_many() it is said that
> > preemption must be disabled during its execution. And that function gets executed
> > among other ways like that:
> > -------------------------->8-----------------------
> >    flush_tlb_range()
> >      -> on_each_cpu_mask()
> >           -> smp_call_function_many()
> > -------------------------->8-----------------------
> 
> In general I prefer not to - Peter what say you ?

The comment with smp_call_function_many() is correct, it relies on
preemption being disabled in a number of ways. I would expect
this_cpu_ptr() for example to complain when used with preemption
enabled (CONFIG_DEBUG_PREEMPT).