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Date: Tue, 24 May 2016 19:13:36 +0300 From: Vladimir Davydov <vdavydov@...tuozzo.com> To: Eric Dumazet <eric.dumazet@...il.com> CC: Andrew Morton <akpm@...ux-foundation.org>, Alexander Viro <viro@...iv.linux.org.uk>, Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, <linux-mm@...ck.org>, <linux-fsdevel@...r.kernel.org>, <netdev@...r.kernel.org>, <x86@...nel.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH RESEND 7/8] pipe: account to kmemcg 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. Thanks, Vladimir > > > + if (memcg_kmem_enabled()) { > > + memcg_kmem_uncharge(page, 0); > > + __ClearPageKmemcg(page); > > + } > > + __SetPageLocked(page); > > + return 0; > > + } > > + return 1; > > +}
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