From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 4 May 2016 15:53:29 +0200 From: Peter Zijlstra Subject: Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency model Message-ID: <20160504135329.GQ3430@twins.programming.kicks-ass.net> References: <20160504123940.GR2749@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20160504123940.GR2749@pathway.suse.cz> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Archive: To: Petr Mladek Cc: Josh Poimboeuf , Jessica Yu , Jiri Kosina , Miroslav Benes , Ingo Molnar , Michael Ellerman , Heiko Carstens , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Vojtech Pavlik , Jiri Slaby , Chris J Arges , Andy Lutomirski List-ID: On Wed, May 04, 2016 at 02:39:40PM +0200, Petr Mladek wrote: > > + * This barrier also ensures that if another CPU goes through the > > + * syscall barrier, sees the TIF_PATCH_PENDING writes in > > + * klp_start_transition(), and calls klp_patch_task(), it also sees the > > + * above write to the target state. Otherwise it can put the task in > > + * the wrong universe. > > + */ > > By other words, it makes sure that klp_patch_task() will assign the > right patch_state. Where klp_patch_task() could not be called > before we set TIF_PATCH_PENDING in klp_start_transition(). > > > + smp_wmb(); > > +} So I've not read the patch; but ending a function with an smp_wmb() feels wrong. A wmb orders two stores, and I feel both stores should be well visible in the same function.