From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-3751024-1517249755-2-7409832428129320266 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.001, RCVD_IN_DNSWL_HI -5, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='US', FromHeader='org', MailFrom='org' X-Spam-charsets: plain='us-ascii' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: linux-api-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1517249755; b=SKs+XI8jPu/sy1MIG2XbodHKPnyOg6tfCoA/DGztS9Y5CTH IK85TUNSU9wnlBFqoRJDmUeGz0KvX5Rxs2rDi8PXlsUEhLxO9p/E6lvRwGtCFhiM eHTVgAsdy0K+hDllJmTvSApP9VUw8A4ERA6ywHUatAetX8Gt/14D6mJaJ8Ipvfj9 fjMm7IQUExlnkSuaFyMRuqV/5p2CK5fK0BWM/HvYsA4ldrTLq61eU1POxiaW9QxR /vWwOe+lwaJINvVdQw/LapFEFzxITKYwSjvB56lmCCpFTDhLjFQOSIJgxSeTcXIn ZTxr9EYsyfLUrjgY2+rsvnoscb6vlnzwtzo2hGw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=date:from:to:cc:subject:message-id :references:mime-version:content-type:in-reply-to:sender :list-id; s=arctest; t=1517249755; bh=V9fWv0oTq/UyltLR0bKZF1CU8q 0r7LTs7S847avhQXQ=; b=BRos7ciTGJz0kvCMHz+F2zmUretyt5ZRQLXWeDr7Vy S6Bpsqfkc9PUyL2G2o1FidvCvZu1KJ7nOjiUlyWjpQb4lyO7sYtQ6SHKpa+mUfpW 1WsAxazZpzCdw7IJUktgoj9i9FU/LWJR3mFAH5+q0toCtvK06mkgZNz31lj7V0Ub N4+OZjRQa72zMnfloYVLB1i1uk6crFK1+aiLfMf6NQ1WBKaCrA+b3qLUy9LDaiL+ 55azZDn+WjV03wik10ufIpAbNleNXjcnlQIcf8CyzOUk7Qfd+Qql2QPTnTzx+MYq 0xDBx7cEK6nluS3u9mF/V8UDWdn7p5worjN2qHiJAeOg== ARC-Authentication-Results: i=1; mx4.messagingengine.com; arc=none (no signatures found); dkim=fail (message has been altered; 2048-bit rsa key sha256) header.d=infradead.org header.i=@infradead.org header.b=M35GDTDo x-bits=2048 x-keytype=rsa x-algorithm=sha256 x-selector=merlin.20170209; dmarc=none (p=none,has-list-id=yes,d=none) header.from=infradead.org; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=linux-api-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=infradead.org header.result=pass header_is_org_domain=yes Authentication-Results: mx4.messagingengine.com; arc=none (no signatures found); dkim=fail (message has been altered; 2048-bit rsa key sha256) header.d=infradead.org header.i=@infradead.org header.b=M35GDTDo x-bits=2048 x-keytype=rsa x-algorithm=sha256 x-selector=merlin.20170209; dmarc=none (p=none,has-list-id=yes,d=none) header.from=infradead.org; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=linux-api-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=infradead.org header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751402AbeA2SPw (ORCPT ); Mon, 29 Jan 2018 13:15:52 -0500 Received: from merlin.infradead.org ([205.233.59.134]:58798 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751072AbeA2SPv (ORCPT ); Mon, 29 Jan 2018 13:15:51 -0500 Date: Mon, 29 Jan 2018 19:15:29 +0100 From: Peter Zijlstra To: Mathieu Desnoyers Cc: Ingo Molnar , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Andy Lutomirski , "Paul E . McKenney" , Boqun Feng , Andrew Hunter , Maged Michael , Avi Kivity , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Dave Watson , "H . Peter Anvin" , Andrea Parri , Russell King , Greg Hackmann , Will Deacon , David Sehr , Linus Torvalds , x86@kernel.org, linux-arch@vger.kernel.org Subject: Re: [PATCH 08/11] membarrier: Provide core serializing command (v2) Message-ID: <20180129181529.GG2295@hirez.programming.kicks-ass.net> References: <20180123155733.3404-1-mathieu.desnoyers@efficios.com> <20180123155733.3404-9-mathieu.desnoyers@efficios.com> <20180129180414.GO2249@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180129180414.GO2249@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Mon, Jan 29, 2018 at 07:04:14PM +0100, Peter Zijlstra wrote: > On Tue, Jan 23, 2018 at 10:57:30AM -0500, Mathieu Desnoyers wrote: > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index f38c4c7e256a..041893128f51 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -2662,9 +2662,13 @@ static struct rq *finish_task_switch(struct task_struct *prev) > > * thread, mmdrop()'s implicit full barrier is required by the > > * membarrier system call, because the current active_mm can > > * become the current mm without going through switch_mm(). > > + * membarrier also requires a core serializing instruction > > + * before going back to user-space after storing to rq->curr. > > */ > > - if (mm) > > + if (mm) { > > + membarrier_mm_sync_core_before_usermode(mm); > > mmdrop(mm); > > + } > > *confused*, when we switch from process A to process B, context_switch() > will not set rq->prev_mm and the above mm will be NULL and we'll not > pass through your_function_names_are_waaay_too_long and we'll not get > cookies. > > And if there's anything more complicated going on, the comment/changelog > are not adequate. Aaah, its the case where we do not pass through switch_mm(), the partial comment got to me. I only realized after reading the next patch. > > if (unlikely(prev_state == TASK_DEAD)) { > > if (prev->sched_class->task_dead) > > prev->sched_class->task_dead(prev); > >