From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755684AbaIBWTc (ORCPT ); Tue, 2 Sep 2014 18:19:32 -0400 Received: from terminus.zytor.com ([198.137.202.10]:40533 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755650AbaIBWT2 (ORCPT ); Tue, 2 Sep 2014 18:19:28 -0400 Date: Tue, 2 Sep 2014 15:19:16 -0700 From: tip-bot for Oleg Nesterov Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, sbsiddha@gmail.com, oleg@redhat.com, tglx@linutronix.de, hpa@linux.intel.com Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, sbsiddha@gmail.com, tglx@linutronix.de, oleg@redhat.com, hpa@linux.intel.com In-Reply-To: <20140902175723.GA21659@redhat.com> References: <20140902175723.GA21659@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/fpu] x86, fpu: copy_process: Avoid fpu_alloc/ copy if !used_math() Git-Commit-ID: f1853505d9ca1c3ea27c29cf83c24661531c527b 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: f1853505d9ca1c3ea27c29cf83c24661531c527b Gitweb: http://git.kernel.org/tip/f1853505d9ca1c3ea27c29cf83c24661531c527b Author: Oleg Nesterov AuthorDate: Tue, 2 Sep 2014 19:57:23 +0200 Committer: H. Peter Anvin CommitDate: Tue, 2 Sep 2014 14:51:16 -0700 x86, fpu: copy_process: Avoid fpu_alloc/copy if !used_math() arch_dup_task_struct() copies thread.fpu if fpu_allocated(), this looks suboptimal and misleading. Say, a forking process could use FPU only once in a signal handler but now tsk_used_math(src) == F, in this case the child gets a copy of fpu->state for no reason. The child won't use the saved registers anyway even if it starts to use FPU, this can only avoid fpu_alloc() in do_device_not_available(). Change this code to check tsk_used_math(current) instead. We still need to clear fpu->has_fpu/state, we could do this memset(0) under fpu_allocated() check but I think this doesn't make sense. See also the next change. use_eager_fpu() assumes that fpu_allocated() is always true, but a forking task (and thus its child) must always have PF_USED_MATH set, otherwise the child can either use FPU without used_math() (note that switch_fpu_prepare() doesn't do stts() in this case), or it will be killed by do_device_not_available()->BUG_ON(use_eager_fpu). Signed-off-by: Oleg Nesterov Link: http://lkml.kernel.org/r/20140902175723.GA21659@redhat.com Reviewed-by: Suresh Siddha Signed-off-by: H. Peter Anvin --- arch/x86/kernel/process.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index f804dc9..b9ba9d5 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -64,14 +64,13 @@ EXPORT_SYMBOL_GPL(task_xstate_cachep); */ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) { - int ret; - *dst = *src; - if (fpu_allocated(&src->thread.fpu)) { - memset(&dst->thread.fpu, 0, sizeof(dst->thread.fpu)); - ret = fpu_alloc(&dst->thread.fpu); - if (ret) - return ret; + + memset(&dst->thread.fpu, 0, sizeof(dst->thread.fpu)); + if (tsk_used_math(src)) { + int err = fpu_alloc(&dst->thread.fpu); + if (err) + return err; fpu_copy(dst, src); } return 0;