linux-kernel - Re: [PATCH] ARM: cache-v7: Disable preemption when reading CCSIDR

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Message-ID: <4F2BC1E1.2080702@ru.mvista.com>
Date:	Fri, 03 Feb 2012 15:15:45 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Nicolas Pitre <nico@...xnic.net>
CC:	Stephen Boyd <sboyd@...eaurora.org>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: cache-v7: Disable preemption when reading CCSIDR

Hello.

On 03-02-2012 7:04, Nicolas Pitre wrote:

>>>>> If you simply disable/restore IRQs around the critical region then you
>>>>> don't have to worry about __v7_setup.  Plus this will allow for
>>>>> v7_flush_dcache_all to still be callable from atomic context.
>>>> Ok. Here's a patch. I still need to test it. I'll send another patch
>>>> series to cleanup the get_thread_info stuff (there's two of them?).
>>>>
>>>>   arch/arm/mm/cache-v7.S |    6 ++++++
>>>>   1 files changed, 6 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/arch/arm/mm/cache-v7.S b/arch/arm/mm/cache-v7.S
>>>> index 07c4bc8..654a5fc 100644
>>>> --- a/arch/arm/mm/cache-v7.S
>>>> +++ b/arch/arm/mm/cache-v7.S
>>>> @@ -54,9 +54,15 @@ loop1:
>>>>   	and	r1, r1, #7			@ mask of the bits for current cache only
>>>>   	cmp	r1, #2				@ see what cache we have at this level
>>>>   	blt	skip				@ skip if no cache, or just i-cache
>>>> +#ifdef CONFIG_PREEMPT
>>>> +	save_and_disable_irqs r9		@ make cssr&csidr read atomic
>>>> +#endif
>>>>   	mcr	p15, 2, r10, c0, c0, 0		@ select current cache level in cssr
>>>>   	isb					@ isb to sych the new cssr&csidr
>>>>   	mrc	p15, 1, r1, c0, c0, 0		@ read the new csidr
>>>> +#ifdef CONFIG_PREEMPT
>>>> +	restore_irqs r9
>>>> +#endif

>>> I'd suggest using restore_irqs_notrace instead.  The IRQ-off period is
>>> so small that there is no point tracing it.

>> Thanks. I'll make sure to do that before uploading to the patch tracker.

> Might be worth flagging this for the stable kernels as well
> (CC: stable@...nel.org).

    The new address is stable@...r.kernel.org as Greg KH wrote.

WBR, Sergei
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