From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DD488C433E2 for ; Thu, 16 Jul 2020 15:53:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9EC0D2064B for ; Thu, 16 Jul 2020 15:53:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="TTVQzQQ8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9EC0D2064B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 39D598D0029; Thu, 16 Jul 2020 11:53:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 34D2E8D0016; Thu, 16 Jul 2020 11:53:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 23C5F8D0029; Thu, 16 Jul 2020 11:53:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0001.hostedemail.com [216.40.44.1]) by kanga.kvack.org (Postfix) with ESMTP id 09B5F8D0016 for ; Thu, 16 Jul 2020 11:53:45 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 89F89180AD802 for ; Thu, 16 Jul 2020 15:53:44 +0000 (UTC) X-FDA: 77044384368.15.back39_4600ddf26f03 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 558A51814B0C1 for ; Thu, 16 Jul 2020 15:53:43 +0000 (UTC) X-HE-Tag: back39_4600ddf26f03 X-Filterd-Recvd-Size: 4332 Received: from mail-ej1-f67.google.com (mail-ej1-f67.google.com [209.85.218.67]) by imf18.hostedemail.com (Postfix) with ESMTP for ; Thu, 16 Jul 2020 15:53:42 +0000 (UTC) Received: by mail-ej1-f67.google.com with SMTP id dp18so7056257ejc.8 for ; Thu, 16 Jul 2020 08:53:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=8WXG2PIfyvvmPCMZWK/gVmBE6W6BlBqBnmsVmBGJnAE=; b=TTVQzQQ8ViT26pmUNnI4AiNVW2VzNBVbcYWM3Gl8mx7rT/pIssKnqsignxE0w8FuXi 3eYXIYONhvl9O6WN+MFAA1B5qMhqm6imyFymvH5wjKTSVktzWmzxkQJTh3fH6AFIWsGU 5nUncZclPPs0cTOIBXHbRadP5rWrTInxmdohCU6TZNwEJ6/COZsIjEV3HNQXbC0R86XM bGDSspfH/2WT3M7Rj4sGmYXfU7wzz3uKyM7DsC5iNURYzvxWpIXNMQtWQZEc4zGy2CfH msueYSKFjXIQBwzUnweSezPrtfjSXzLbN8fiImPnjktGXVBRrPy4jup5lOuplPJOgG0F DMGg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=8WXG2PIfyvvmPCMZWK/gVmBE6W6BlBqBnmsVmBGJnAE=; b=GYCD/upCKFxLpzhR3t65jZ2UHKpQlIifthpdgElKLd6Y4GiKqbx25M/frc75grl+sV cW8Q0fHcrvSskCFOKWC8ZXkwzK+8zAUxALk+v9zahsYwJZIsBvVZ4WXWJh29j62KXMhZ 9KgTojGH8wiBv5tecVC/noWFdJ5kz51TTa5jd+oNkgWUZGfGggNrgt0fl5W9EY2ud5pN 6LVxbVdFOlmv5ZxhQWqq4vyt8P0XUauxU3HarUkkhz+3KHYesb0B99fNOS0fmtjIB6qJ ksjNSnowUF/7oDFOtL88jrSrshRTAjY7DTMwXaaoRpQQaQIzJbMo7+JqWBaNpaAliIGT U4zw== X-Gm-Message-State: AOAM530M3fBv6bCg7h0Qbfb7HU51JOqkhpd8NLBzHzl9WMo8+0Oxf2ht cPFfx/o5gB8NmabuOUWIAKIyrzMoE9bTnn5PTlYvoohx X-Google-Smtp-Source: ABdhPJyC/kYBgU3IOAczrEfawy9HqiaBTF+01y7Bb6pDO746HsQJM5cE84Bpja/aFZhr/N9Gx94sJ9OFb9TOk4ri9JA= X-Received: by 2002:a17:906:6d56:: with SMTP id a22mr4555135ejt.440.1594914821045; Thu, 16 Jul 2020 08:53:41 -0700 (PDT) MIME-Version: 1.0 References: <20200716060553.24618-1-ebiggers@kernel.org> In-Reply-To: <20200716060553.24618-1-ebiggers@kernel.org> From: Dan Williams Date: Thu, 16 Jul 2020 08:53:30 -0700 Message-ID: Subject: Re: [PATCH] /dev/mem: Add missing memory barriers for devmem_inode To: Eric Biggers Cc: Arnd Bergmann , Greg Kroah-Hartman , Linux Kernel Mailing List , Linux MM , Ingo Molnar , Kees Cook , Matthew Wilcox , Russell King , Andrew Morton Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 558A51814B0C1 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jul 15, 2020 at 11:07 PM Eric Biggers wrote: > > From: Eric Biggers > > WRITE_ONCE() isn't the correct way to publish a pointer to a data > structure, since it doesn't include a write memory barrier. Therefore > other tasks may see that the pointer has been set but not see that the > pointed-to memory has finished being initialized yet. Instead a > primitive with "release" semantics is needed. > > Use smp_store_release() for this. > > The use of READ_ONCE() on the read side is still potentially correct if > there's no control dependency, i.e. if all memory being "published" is > transitively reachable via the pointer itself. But this pairing is > somewhat confusing and error-prone. So just upgrade the read side to > smp_load_acquire() so that it clearly pairs with smp_store_release(). > > Cc: Dan Williams > Cc: Arnd Bergmann > Cc: Ingo Molnar > Cc: Kees Cook > Cc: Matthew Wilcox > Cc: Russell King > Cc: Andrew Morton > Cc: Greg Kroah-Hartman > Fixes: 3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims the region") > Signed-off-by: Eric Biggers Makes sense: Acked-by: Dan Williams