From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-3723103-1517249103-2-6832431348330832718 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=1517249102; b=R2yVwM41Tg0DhJ7cM4Kl+4xFi8t1RHgrMoruvo61ICABZmL xHn18Egi4A1UTEiihrCTgVHlh+zWO7Zjs7gCGuNxi6m1jztXOjrMKbxds3dY46FR Zsga1phljekO5SAs5d/4QHX1jmFMVpBW+JwbNlgKWywtbhhKKU9hjrXxh1++7Myn W/iugxlzU/+BqsHyulY4bAOYQfNbmTZ6DjrdGZgBwj97inc7Ny7znQMAin9gv21G wcfZrpyQ5z2iD04/pY9J0W+ZsppBHSoOQ62m5O7M0HXUiIKdpya6ZYRjK+5Gk/RW CvEHEJUXVcbYSKiie7+rnrMvdUJL8FpOZlyox0Q== 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=1517249102; bh=b5vK2wRxJJRQJnxF8uWZLdPstu 3G2SijLhVpOolYovU=; b=WtAhSh/Bcz0H7qyMqBQHhX1ZUK9rG981rxqOGpTCee RgYX1+qhklq3bwCvcbrEYDmtVWk5Klzll3vjVV9pSnDpKeMMwObBjJxlv4X0fGiZ RUJEjohI+HWtQZoTHgLu/ms19ZOFHu7T6dokNwV/bcjccxYcQe4LEJpmzxa23ueV 6tQvPRzoGjAHPylWNnJ0EYkyOMFoXEuctenl+L2VvSq6XrQIGovRbU5vRmSQ5qtL h3RKiCgIezDyDyMTEpWlYudYl0sgBFmFZbyD5PVwgnO834/iqBzc+3fpaYtZIybC 1zw2tE8xDtmtSmGYI9zmgEdDnNRXQ4KN2QsIQLbc4haQ== ARC-Authentication-Results: i=1; mx3.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=oOkP9vw7 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: mx3.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=oOkP9vw7 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 S1751355AbeA2SE7 (ORCPT ); Mon, 29 Jan 2018 13:04:59 -0500 Received: from merlin.infradead.org ([205.233.59.134]:58708 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751072AbeA2SE6 (ORCPT ); Mon, 29 Jan 2018 13:04:58 -0500 Date: Mon, 29 Jan 2018 19:04:14 +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: <20180129180414.GO2249@hirez.programming.kicks-ass.net> References: <20180123155733.3404-1-mathieu.desnoyers@efficios.com> <20180123155733.3404-9-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180123155733.3404-9-mathieu.desnoyers@efficios.com> 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 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. > if (unlikely(prev_state == TASK_DEAD)) { > if (prev->sched_class->task_dead) > prev->sched_class->task_dead(prev);