From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?utf-8?B?SsO2cm4=?= Engel Subject: Re: [PATCH] sg: atomize check and set sdp->exclude in sg_open Date: Wed, 5 Jun 2013 11:41:07 -0400 Message-ID: <20130605154106.GA2737@logfs.org> References: <51AF0269.9070900@oracle.com> <20130605132746.GA1690@logfs.org> <51AF646D.7030903@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <51AF646D.7030903@oracle.com> Sender: linux-kernel-owner@vger.kernel.org To: vaughan Cc: dgilbert@interlog.com, JBottomley@parallels.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org On Thu, 6 June 2013 00:16:45 +0800, vaughan wrote: > =E4=BA=8E 2013=E5=B9=B406=E6=9C=8805=E6=97=A5 21:27, J=C3=B6rn Engel = =E5=86=99=E9=81=93: > >On Wed, 5 June 2013 17:18:33 +0800, vaughan wrote: > >> > >>Check and set sdp->exclude should be atomic when set in sg_open(). > > > >The patch is line-wrapped. More importantly, it doesn't seem to do > It's shorter than the original line, so I just leave it like this... Sure. What I meant by line-wrapped is that your mailer mangled the patch. Those two lines should have been one: > >>- ((!sfds_list_empty(sdp) || get_exclude(sdp)= ) > >>? 0 : set_exclude(sdp, 1))); > >what your description indicates it should do. And lastly, does this > >fix a bug, possibly even one you have a testcase for, or was it foun= d > >by code inspection? > I found it by code inspection. A race condition may happen with the > old code if two threads are both trying to open the same sg with > O_EXCL simultaneously. It's possible that they both find fsds list > is empty and get_exclude(sdp) returns 0, then they both call > set_exclude() and break out from wait_event_interruptible and resume > open. So it's necessary to check again with sg_open_exclusive_lock > held to ensure only one can set sdp->exclude and return >0 to break > out from wait_event loop. Makes sense. And reading the code again, I have to wonder what monkey came up with the get_exclude/set_exclude functions. Can I sucker you into a slightly larger cleanup? I think the entire "get_exclude(sdp)) ? 0 : set_exclude(sdp, 1)" should be simplified. And once you add the try_set_exclude(), set_exclude will only ever do clear_exclude, so you might as well rename and simplify that as well. Let no good deed go unpunished. J=C3=B6rn -- It's just what we asked for, but not what we want! -- anonymous