linux-kernel - Re: [PATCH] x86/fpu: drop_fpu() should not assume that tsk == current

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Message-ID: <54FDDA09.3050003@redhat.com>
Date:	Mon, 09 Mar 2015 13:36:09 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...nel.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pekka Riikonen <priikone@....fi>,
	Suresh Siddha <sbsiddha@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Subject: Re: [PATCH] x86/fpu: drop_fpu() should not assume that tsk == current

On 03/09/2015 01:10 PM, Oleg Nesterov wrote:
> drop_fpu() does clear_used_math() and usually this is correct because
> tsk == current. However switch_fpu_finish()->restore_fpu_checking() is
> called before it updates the "current_task" variable. If it fails, we
> will wrongly clear the PF_USED_MATH flag of the previous task.

Ouch. Good catch.

> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Cc: <stable@...r.kernel.org>

Reviewed-by: Rik van Riel <riel@...hat.com>

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