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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 EE88AC43603 for ; Thu, 5 Dec 2019 13:06:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BE7F924249 for ; Thu, 5 Dec 2019 13:06:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VFAhQkOl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729497AbfLENGn (ORCPT ); Thu, 5 Dec 2019 08:06:43 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:21262 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729443AbfLENGl (ORCPT ); Thu, 5 Dec 2019 08:06:41 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1575551200; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pIbfnsWyjUzYuMMUtvP8cBzLFVnihHBsEg4LNJqdKgI=; b=VFAhQkOliGfW0YrTIpq45VNIS6YzkAjf04TVvwaK3DxhQSIVqJvchDydPEGe+LsdstTBE6 nCBpucYKeSNa0sKenKTV2CLUvjfh5sz8sfZ0q2q3Gd6MF0DhbC+OHFLcxx1UAE0FYrWdfZ fN6fTMl9tgwUD9RS+luCUFU5LTo4/4Q= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-68-7hcZwkCJNWex1a5zYOwlZw-1; Thu, 05 Dec 2019 08:06:37 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8EC6CDB35; Thu, 5 Dec 2019 13:06:34 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-250.rdu2.redhat.com [10.10.120.250]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6179260135; Thu, 5 Dec 2019 13:06:31 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20191205072838.GA3237@sol.localdomain> References: <20191205072838.GA3237@sol.localdomain> <000000000000a376820598b2eb97@google.com> <20191205054023.GA772@sol.localdomain> To: Eric Biggers Cc: dhowells@redhat.com, amit@kernel.org, arnd@arndb.de, syzbot , gregkh@linuxfoundation.org, jannh@google.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, miklos@szeredi.hu, rostedt@goodmis.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, virtualization@lists.linux-foundation.org, willy@infradead.org Subject: Re: kernel BUG at fs/pipe.c:LINE! MIME-Version: 1.0 Content-ID: <27080.1575551190.1@warthog.procyon.org.uk> Date: Thu, 05 Dec 2019 13:06:30 +0000 Message-ID: <27081.1575551190@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-MC-Unique: 7hcZwkCJNWex1a5zYOwlZw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Eric Biggers wrote: > static __poll_t > pipe_poll(struct file *filp, poll_table *wait) > { > __poll_t mask; > struct pipe_inode_info *pipe =3D filp->private_data; > unsigned int head =3D READ_ONCE(pipe->head); > unsigned int tail =3D READ_ONCE(pipe->tail); >=20 > poll_wait(filp, &pipe->wait, wait); >=20 > BUG_ON(pipe_occupancy(head, tail) > pipe->ring_size); >=20 > It's not holding the pipe mutex, right? So 'head', 'tail' and 'ring_size= ' can > all be changed concurrently, and they aren't read atomically with respect= to > each other. >=20 > How do you propose to implement poll() correctly with the new head + tail > approach? Just take the mutex? Firstly, the BUG_ON() check probably isn't necessary here - the same issue with occupancy being seen to be greater than the queue depth existed previously (there was no locking around the read of pipe->nrbufs and pipe->buffers). I added a sanity check. Secondly, it should be possible to make it such that just the spinlock suffices. The following few patches make the main pipe read/write routines use the spinlock so as not to be interfered with by notification insertion. I didn't roll the spinlock out to splice and suchlike since I prohibit splicing to a notifications pipe because of the iov_iter_revert() fun. David