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=-2.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 C1C50C43381 for ; Mon, 18 Feb 2019 10:47:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C8E42147A for ; Mon, 18 Feb 2019 10:47:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550486853; bh=SP74pSR2WXcfY2R64lXSZRkKL70o8xEOEG3bTFz4noU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Yt9VdD5ltb5ubRMxsLmKpJGJRBhQSOIUuyDUwsuG/WT9s+ltFIa+etQioRrPHgeTQ Hjioorr1+St8tVf/oVsQs1PCo6CwURGNkaeEnyhb9mSuTeDCR+KRydcpu0T3yRQzxq EnGmk0Em6xCGp4VN7j20r27er+IxG7Q9qqOcwbyo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730204AbfBRKrc (ORCPT ); Mon, 18 Feb 2019 05:47:32 -0500 Received: from mail-pf1-f193.google.com ([209.85.210.193]:40153 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728258AbfBRKrb (ORCPT ); Mon, 18 Feb 2019 05:47:31 -0500 Received: by mail-pf1-f193.google.com with SMTP id h1so8364718pfo.7 for ; Mon, 18 Feb 2019 02:47:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=C5GbvVFIVg97XioJPDlPOI1anGzy2w+IqWN8b4+VrMc=; b=ad2Bg3/52cekWVUyCUDtgIXxJyRlvipR9woEtuEKThXVZZROgWE51KmNGZx66k0tal OY7KbMsGo38HkqCOtqHw7YelMS5DnYQ/8si3Sx8oIWwerAIHkUNJbfTQGI8f/vkkt+1y bwfYW3ncDTJoNaAMIc8ZUKAdvhkbW2D1bghjqTYPraS5gSNmmCJ+SVtVvR7j2aPTYceY 0tOXqAJMVogCLoOPnFXH8RniZDyYAVAmoBRZSBPkkmzMtQON9HAuB9fUmRd4WJBZsAwg /JfHpoqEJGeoGy+yzOiB2T5FzGyzlsSrQDO269eGYMkXOlY53dzifwm5jtk0uMZIJLal hYVA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition :content-transfer-encoding:in-reply-to:user-agent; bh=C5GbvVFIVg97XioJPDlPOI1anGzy2w+IqWN8b4+VrMc=; b=UwzDIrekw4SYN1an76nOKudXvbrydFRyP0vs5aHtIbe8P9SdBUAwpaf6L4BF/4lfwC J5WUkr8oS/+gPxx5M40ne7jlu9F55JFL6HI0M6vl7BrQEnMz6B9lT3VDZCqwF+rO/ptI QqNDZ/W56KIUurBkgmPRkkOGW5q+bVTK7NpILJwx6Yu0i1vNKsjo5WVKMGQg3VuOrpCX 1CEEXhJigwNGgX/1Ab3j9YKXtRYPEMEYUZz20QfpbEMkVwjWJqgYYXXNvjKL+yO2ggWW wlfOH5pFQaU5uHcG8Mti26QAR3k65H33sHtCKxKvAu8hBISB7lgqx4djYm3i5/gf1H6j clFQ== X-Gm-Message-State: AHQUAuZzu04NPM1+9kursKEBRfaPOE1JOR600PND48BckpZr+cTHYr9Z vvmXZzd0PLEc/MZxSZwmRbcYaxaZ X-Google-Smtp-Source: AHgI3IYIVeDAtGi6u+93cnNKAR/vWs5JzVyZq0HUoGPZov8zz4Sh+QRxtIVs2kZE4vQdJnXIqY30oA== X-Received: by 2002:a63:65c7:: with SMTP id z190mr18232408pgb.249.1550486850688; Mon, 18 Feb 2019 02:47:30 -0800 (PST) Received: from google.com ([2401:fa00:d:0:98f1:8b3d:1f37:3e8]) by smtp.gmail.com with ESMTPSA id 145sm2897876pgb.66.2019.02.18.02.47.27 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 18 Feb 2019 02:47:29 -0800 (PST) Date: Mon, 18 Feb 2019 19:47:25 +0900 From: Minchan Kim To: Greg KH Cc: LKML , Todd Kjos , Martijn Coenen , Arve =?iso-8859-1?B?SGr4bm5lduVn?= Subject: Re: [PATCH] binder: reduce mmap_sem write-side lock Message-ID: <20190218104725.GA160999@google.com> References: <20190218081145.86633-1-minchan@kernel.org> <20190218083208.GA20069@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190218083208.GA20069@kroah.com> User-Agent: Mutt/1.10.1+60 (6df12dc1) (2018-08-07) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 18, 2019 at 09:32:08AM +0100, Greg KH wrote: > On Mon, Feb 18, 2019 at 05:11:45PM +0900, Minchan Kim wrote: > > binder has used write-side mmap_sem semaphore to release memory > > mapped at address space of the process. However, right lock to > > release pages is down_read, not down_write because page table lock > > already protects the race for parallel freeing. > > > > Please do not use mmap_sem write-side lock which is well known > > contented lock. > > > > Cc: Todd Kjos > > Cc: Martijn Coenen > > Cc: Arve Hjønnevåg > > Cc: Greg Kroah-Hartman > > Signed-off-by: Minchan Kim > > --- > > drivers/android/binder_alloc.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > Is this just needed for the recent binder changes that are in > linux-next, or for older kernels as well? It has been there for several years but no need to fix older kernels because down_write of mmap_sem is technically not a bug to stop the working of binder. Rather than, it's just abuse of the lock so it's okay to fix only recent kernel. Thanks.