From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753302AbbBSLdB (ORCPT ); Thu, 19 Feb 2015 06:33:01 -0500 Received: from terminus.zytor.com ([198.137.202.10]:53022 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753275AbbBSLc6 (ORCPT ); Thu, 19 Feb 2015 06:32:58 -0500 Date: Thu, 19 Feb 2015 03:32:40 -0800 From: tip-bot for Oleg Nesterov Message-ID: Cc: bp@suse.de, mingo@kernel.org, oleg@redhat.com, tglx@linutronix.de, linux-kernel@vger.kernel.org, hpa@zytor.com, torvalds@linux-foundation.org, riel@redhat.com Reply-To: torvalds@linux-foundation.org, riel@redhat.com, tglx@linutronix.de, hpa@zytor.com, linux-kernel@vger.kernel.org, mingo@kernel.org, oleg@redhat.com, bp@suse.de In-Reply-To: <1423252925-14451-3-git-send-email-riel@redhat.com> References: <1423252925-14451-3-git-send-email-riel@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/fpu] x86/fpu: Don't do __thread_fpu_end() if use_eager_fpu() Git-Commit-ID: 1a2a7f4ec8e3a7ac582dac4d01fcc7e8acd3bb30 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 1a2a7f4ec8e3a7ac582dac4d01fcc7e8acd3bb30 Gitweb: http://git.kernel.org/tip/1a2a7f4ec8e3a7ac582dac4d01fcc7e8acd3bb30 Author: Oleg Nesterov AuthorDate: Fri, 6 Feb 2015 15:01:59 -0500 Committer: Borislav Petkov CommitDate: Thu, 19 Feb 2015 11:12:46 +0100 x86/fpu: Don't do __thread_fpu_end() if use_eager_fpu() unlazy_fpu()->__thread_fpu_end() doesn't look right if use_eager_fpu(). Unconditional __thread_fpu_end() is only correct if we know that this thread can't return to user-mode and use FPU. Fortunately it has only 2 callers. fpu_copy() checks use_eager_fpu(), and init_fpu(current) can be only called by the coredumping thread via regset->get(). But it is exported to modules, and imo this should be fixed anyway. And if we check use_eager_fpu() we can use __save_fpu() like fpu_copy() and save_init_fpu() do. - It seems that even !use_eager_fpu() case doesn't need the unconditional __thread_fpu_end(), we only need it if __save_init_fpu() returns 0. - It is still not clear to me if __save_init_fpu() can safely nest with another save + restore from __kernel_fpu_begin(). If not, we can use kernel_fpu_disable() to fix the race. Signed-off-by: Oleg Nesterov Signed-off-by: Rik van Riel Cc: Linus Torvalds Link: http://lkml.kernel.org/r/1423252925-14451-3-git-send-email-riel@redhat.com Signed-off-by: Borislav Petkov --- arch/x86/kernel/i387.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index 4d0db9e..f3ced6f 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -106,8 +106,12 @@ void unlazy_fpu(struct task_struct *tsk) { preempt_disable(); if (__thread_has_fpu(tsk)) { - __save_init_fpu(tsk); - __thread_fpu_end(tsk); + if (use_eager_fpu()) { + __save_fpu(tsk); + } else { + __save_init_fpu(tsk); + __thread_fpu_end(tsk); + } } preempt_enable(); }