From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752585AbbATOQ5 (ORCPT ); Tue, 20 Jan 2015 09:16:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39506 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752190AbbATOP6 (ORCPT ); Tue, 20 Jan 2015 09:15:58 -0500 Message-ID: <54BE630E.4000901@redhat.com> Date: Tue, 20 Jan 2015 09:15:42 -0500 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Oleg Nesterov , Linus Torvalds , Suresh Siddha CC: linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, matt.fleming@intel.com, bp@suse.de, pbonzini@redhat.com, tglx@linutronix.de, luto@amacapital.net Subject: Re: [PATCH 1/3] x86, fpu: __kernel_fpu_begin() should clear fpu_owner_task even if use_eager_fpu() References: <1421012793-30106-1-git-send-email-riel@redhat.com> <20150115191918.GA27332@redhat.com> <20150119185109.GA16427@redhat.com> <20150119185132.GB16427@redhat.com> In-Reply-To: <20150119185132.GB16427@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/19/2015 01:51 PM, Oleg Nesterov wrote: > __kernel_fpu_begin() does nothing if !__thread_has_fpu() && use_eager_fpu(), > perhaps it assumes that this case is simply impossible. This is certainly > not possible if in_interrupt() == T; interrupted_user_mode() should have > FPU, and interrupted_kernel_fpu_idle() should fail if !__thread_has_fpu(). > > However, even if use_eager_fpu() == T a task can do drop_fpu(), then switch > to another thread which becomes fpu_owner_task, then resume and call some > function which does kernel_fpu_begin(). Say, an exiting task does a lot of > things after exit_thread(), it is not safe to assume that it can't use FPU > in these paths. > > Signed-off-by: Oleg Nesterov Reviewed-by: Rik van Riel