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Date: Wed, 5 Feb 2014 22:26:24 -0700 (MST)
From: Nate Eldredge <nate@thatsmathematics.com>
To: Suresh Siddha <sbsiddha@gmail.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	stable <stable@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Maarten Baert <maarten-baert@hotmail.com>,
	Jan Kara <jack@suse.cz>, George Spelvin <linux@horizon.com>,
	Pekka Riikonen <priikone@iki.fi>
Subject: Re: [PATCH] Make math_state_restore() save and restore the interrupt
 flag
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On Sun, 2 Feb 2014, Suresh Siddha wrote:

> Here is the second patch, which should fix the issue reported in this
> thread. Maarten, Nate, George, please give this patch a try as is and
> see if it helps address the issue you ran into. And please ack/review
> with your test results.

3.13 plus this patch: boots and fixes the testcase I reported (core dump 
on ecrypt).

Tested-by: Nate Eldredge <nate@thatsmathematics.com>

> diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
> index 4e5f770..670bba1 100644
> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -87,10 +87,19 @@ EXPORT_SYMBOL(__kernel_fpu_begin);
>
> void __kernel_fpu_end(void)
> {
> -	if (use_eager_fpu())
> -		math_state_restore();
> -	else
> +	if (use_eager_fpu()) {
> +		/*
> +		 * For eager fpu, most the time, tsk_used_math() is true.
> +		 * Restore the user math as we are done with the kernel usage.
> +		 * At few instances during thread exit, signal handling etc,
> +		 * tsk_used_math() is false. Those few places will take proper
> +		 * actions, so we don't need to restore the math here.
> +		 */
> +		if (likely(tsk_used_math(current)))
> +			math_state_restore();
> +	} else {
> 		stts();
> +	}
> }
> EXPORT_SYMBOL(__kernel_fpu_end);

-- 
Nate Eldredge
nate@thatsmathematics.com