From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ Date: Thu, 31 Jul 2014 18:58:04 +0200 Message-ID: <20140731165804.GB16800@redhat.com> References: <7123b2489cc5d1d5abb7bcf1364ca729cab3e6ca.1406604806.git.luto@amacapital.net> <20140729193232.GA8153@redhat.com> <20140730164344.GA27954@localhost.localdomain> <20140731151630.GA7842@localhost.localdomain> <20140731164246.GA15974@redhat.com> <20140731164918.GC7842@localhost.localdomain> <20140731165423.GA16800@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20140731165423.GA16800@redhat.com> Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Frederic Weisbecker Cc: Andy Lutomirski , "linux-kernel@vger.kernel.org" , Kees Cook , Will Drewry , X86 ML , "linux-arm-kernel@lists.infradead.org" , Linux MIPS Mailing List , linux-arch , LSM List , Alexei Starovoitov , "H. Peter Anvin" List-Id: linux-arch.vger.kernel.org On 07/31, Oleg Nesterov wrote: > > On 07/31, Frederic Weisbecker wrote: > > > > On Thu, Jul 31, 2014 at 06:42:46PM +0200, Oleg Nesterov wrote: > > > > > > And if we change this, then the code above becomes racy. The state of > > > TIF_XYZ can be changed right after the check. OK, it is racy anyway ;) > > > but still this adds more confusion. > > > > No because all running tasks have this flag set when context tracking is > > enabled. And context tracking can't be disabled on runtime. > > Yes, yes, please note that I said "if we change this". And "it is racy anyway" connects to the problems we discuss in another thread. Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:61968 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751412AbaGaRA2 (ORCPT ); Thu, 31 Jul 2014 13:00:28 -0400 Date: Thu, 31 Jul 2014 18:58:04 +0200 From: Oleg Nesterov Subject: Re: [PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ Message-ID: <20140731165804.GB16800@redhat.com> References: <7123b2489cc5d1d5abb7bcf1364ca729cab3e6ca.1406604806.git.luto@amacapital.net> <20140729193232.GA8153@redhat.com> <20140730164344.GA27954@localhost.localdomain> <20140731151630.GA7842@localhost.localdomain> <20140731164246.GA15974@redhat.com> <20140731164918.GC7842@localhost.localdomain> <20140731165423.GA16800@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140731165423.GA16800@redhat.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Frederic Weisbecker Cc: Andy Lutomirski , "linux-kernel@vger.kernel.org" , Kees Cook , Will Drewry , X86 ML , "linux-arm-kernel@lists.infradead.org" , Linux MIPS Mailing List , linux-arch , LSM List , Alexei Starovoitov , "H. Peter Anvin" Message-ID: <20140731165804.MVBfnKq5DNJOzx4oekRaECA_ZPnI1G17BCRlUtLcvjA@z> On 07/31, Oleg Nesterov wrote: > > On 07/31, Frederic Weisbecker wrote: > > > > On Thu, Jul 31, 2014 at 06:42:46PM +0200, Oleg Nesterov wrote: > > > > > > And if we change this, then the code above becomes racy. The state of > > > TIF_XYZ can be changed right after the check. OK, it is racy anyway ;) > > > but still this adds more confusion. > > > > No because all running tasks have this flag set when context tracking is > > enabled. And context tracking can't be disabled on runtime. > > Yes, yes, please note that I said "if we change this". And "it is racy anyway" connects to the problems we discuss in another thread. Oleg.