linux-kernel - Re: [PATCH] x86-64, espfix: consider IRQs are off when initializing

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Date:	Thu, 17 Jul 2014 11:58:42 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86-64, espfix: consider IRQs are off when initializing

On 07/17/2014 11:48 AM, H. Peter Anvin wrote:
> On 07/17/2014 08:13 AM, Sasha Levin wrote:
>> > When going through our initialization code (init_espfix_ap() ) we need to
>> > keep in mind IRQs are off, and we need to handle it appropriately:
>> > 
>> >  - Do not allocate with __GFP_FS.
>> >  - No point in using a mutex.
>> > 
>> > Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
> I don't think this is safe.  The whole point was that if we do
> GFP_ATOMIC we have to accept failure, and if we have a spin lock then
> sleeping is not permitted.  It is unclear to me is sleeping is safe in
> this context even so, so we may still have a problem, but calling
> __get_free_page(GFP_ATOMIC) and then unconditionally use the results is
> not right.

This is the result of getting an error message for allocating with GFP_KERNEL
saying that we can't do that with IRQs off.

My assumption after that was that we're not going to be sleeping at all, which
is why spinlock/GFP_ATOMIC would be correct here.


Thanks,
Sasha
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