linux-kernel - Re: [PATCH] arm64: abort counter_read_on_cpu() when irqs

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Message-ID: <20201113195532.GA20519@gaia>
Date:   Fri, 13 Nov 2020 19:55:33 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Ionela Voinescu <ionela.voinescu@....com>
Cc:     Mark Rutland <mark.rutland@....com>, sudeep.holla@....com,
        will@...nel.org, morten.rasmussen@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled()

On Fri, Nov 13, 2020 at 04:58:43PM +0000, Ionela Voinescu wrote:
> On Friday 13 Nov 2020 at 16:02:34 (+0000), Mark Rutland wrote:
> > On Fri, Nov 13, 2020 at 03:53:28PM +0000, Ionela Voinescu wrote:
> > > Given that smp_call_function_single() can deadlock when interrupts are
> > > disabled, abort the SMP call if irqs_disabled(). This scenario is
> > > currently not possible given the function's uses, but safeguard this for
> > > potential future uses.
> > 
> > Sorry to contradict earlier feedback, but I think this is preferable
> > as-is, since smp_call_function_single() will
> > WARN_ON_ONCE(irqs_disabled())), but this will silently mask any dodgy
> > usage.
> 
> Probably it only contradicts the chosen implementation.
> 
> > If we want a separate check here, I reckon we should wrap it with a
> > WARN_ON_ONCE(), and only relax that if/when we have a legitimate case
> > for calling this with IRQs disabled.
> > 
> 
> That's fair. I'll replace the condition below with:
> 
> 	if (!cpu_has_amu_feat(cpu))
> 		return -EOPNOTSUPP;
> 
> 	if (WARN_ON_ONCE(irqs_disabled())
> 		return -EPERM;

Works for me. Thanks.

-- 
Catalin