From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756140AbbCMRcy (ORCPT ); Fri, 13 Mar 2015 13:32:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56055 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752090AbbCMRcx (ORCPT ); Fri, 13 Mar 2015 13:32:53 -0400 Date: Fri, 13 Mar 2015 18:30:30 +0100 From: Oleg Nesterov To: Dave Hansen , Borislav Petkov , Ingo Molnar Cc: Andy Lutomirski , Linus Torvalds , Pekka Riikonen , Rik van Riel , Suresh Siddha , LKML , "Yu, Fenghua" , Quentin Casasnovas Subject: [PATCH v2 4/4] x86/fpu: don't abuse drop_init_fpu() in flush_thread() Message-ID: <20150313173030.GA31217@redhat.com> References: <54F74F59.5070107@intel.com> <20150311173346.GB5032@redhat.com> <20150311173507.GF5032@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150311173507.GF5032@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org flush_thread() -> drop_init_fpu() is suboptimal and confusing. It does drop_fpu() or restore_init_xstate() depending on !use_eager_fpu(). But flush_thread() too checks eagerfpu right after that, and if it is true then restore_init_xstate() just burns CPU for no reason. We are going to load init_xstate_buf again after we set used_math/user_has_fpu, until then the FPU state can't survive after switch_to(). Remove it, and change the "if (!use_eager_fpu())" to call drop_fpu(). While at it, clean up the tsk/current usage. Signed-off-by: Oleg Nesterov --- arch/x86/kernel/process.c | 15 ++++++--------- 1 files changed, 6 insertions(+), 9 deletions(-) diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index c396de2..c236306 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -131,17 +131,14 @@ void flush_thread(void) flush_ptrace_hw_breakpoint(tsk); memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array)); - drop_init_fpu(tsk); - /* - * Free the FPU state for non xsave platforms. They get reallocated - * lazily at the first use. - */ - if (!use_eager_fpu()) + if (!use_eager_fpu()) { + /* FPU state will be reallocated lazily at the first use. */ + drop_fpu(tsk); free_thread_xstate(tsk); - else if (!used_math()) { + } else if (!used_math()) { /* kthread execs. TODO: cleanup this horror. */ - if (WARN_ON(init_fpu(current))) - force_sig(SIGKILL, current); + if (WARN_ON(init_fpu(tsk))) + force_sig(SIGKILL, tsk); user_fpu_begin(); restore_init_xstate(); } -- 1.5.5.1