From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id D2EBA6B0005 for ; Tue, 24 May 2016 16:04:37 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id 203so48981933pfy.2 for ; Tue, 24 May 2016 13:04:37 -0700 (PDT) Received: from mail-pf0-x229.google.com (mail-pf0-x229.google.com. [2607:f8b0:400e:c00::229]) by mx.google.com with ESMTPS id f1si873239pfc.216.2016.05.24.13.04.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 May 2016 13:04:36 -0700 (PDT) Received: by mail-pf0-x229.google.com with SMTP id b124so10166951pfb.0 for ; Tue, 24 May 2016 13:04:36 -0700 (PDT) Message-ID: <1464120273.5939.53.camel@edumazet-glaptop3.roam.corp.google.com> Subject: Re: [PATCH RESEND 7/8] pipe: account to kmemcg From: Eric Dumazet Date: Tue, 24 May 2016 13:04:33 -0700 In-Reply-To: <20160524161336.GA11150@esperanza> References: <2c2545563b6201f118946f96dd8cfc90e564aff6.1464079538.git.vdavydov@virtuozzo.com> <1464094742.5939.46.camel@edumazet-glaptop3.roam.corp.google.com> <20160524161336.GA11150@esperanza> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: Andrew Morton , Alexander Viro , Johannes Weiner , Michal Hocko , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org On Tue, 2016-05-24 at 19:13 +0300, Vladimir Davydov wrote: > On Tue, May 24, 2016 at 05:59:02AM -0700, Eric Dumazet wrote: > ... > > > +static int anon_pipe_buf_steal(struct pipe_inode_info *pipe, > > > + struct pipe_buffer *buf) > > > +{ > > > + struct page *page = buf->page; > > > + > > > + if (page_count(page) == 1) { > > > > This looks racy : some cpu could have temporarily elevated page count. > > All pipe operations (pipe_buf_operations->get, ->release, ->steal) are > supposed to be called under pipe_lock. So, if we see a pipe_buffer->page > with refcount of 1 in ->steal, that means that we are the only its user > and it can't be spliced to another pipe. > > In fact, I just copied the code from generic_pipe_buf_steal, adding > kmemcg related checks along the way, so it should be fine. So you guarantee that no other cpu might have done get_page_unless_zero() right before this test ? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org