linux-kernel - Re: [PATCH -rt] ARM TLB flush fix: don't forget to re-enable preemption

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Date:	Wed, 23 May 2007 10:31:17 -0700
From:	Kevin Hilman <khilman@...sta.com>
To:	Kevin Hilman <khilman@...sta.com>,
	Daniel Walker <dwalker@...sta.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -rt] ARM TLB flush fix: don't forget to re-enable preemption

Russell King wrote:
> On Wed, May 23, 2007 at 09:13:57AM -0700, Kevin Hilman wrote:
>> On Wed, 2007-05-23 at 10:22 +0100, Russell King wrote:
>>> In which case shouldn't it be at the end of the function so it includes
>>> the write buffer handling as well?
>>>
>>> However, I think I agree with Daniel on this one.  I don't see the point
>>> of the preempt_disable() here.
>> Note that my patch simply adds an enable to match the disable added by
>> the -rt patch.  I'm not sure where the disable originally came from, but
>> there are disable/enable pairs scattered throughout tlbflush.h in the
>> -rt patch.
>>
>> If this one isn't necessary, then the others probably are not either.
>> In most cases there are 2 mcr instructions inside the critical section.
>> One for the dsb() and the other for the actual function.
>>
>> Russell, is there a reason any of these sections should be atomic?
> 
> I don't see any reason for them to be - when switching to another process
> we'll generally do a full TLB flush anyway, so what's the point in making
> these flushes atomic?

OK, I've removed the locally and will be doing some testing on OMAP2
(ARMv6.)  I'll submit a patch to Ingo if things look good.

In the meantime, my previous fix is still necessary for -rt to even work
on ARM.

Kevin
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