From mboxrd@z Thu Jan 1 00:00:00 1970 From: Janak Desai Subject: Re: [PATCH] New System call unshare (try 2) Date: Thu, 13 Oct 2005 09:27:18 -0400 Message-ID: <434E60B6.7030803@us.ibm.com> References: <20051012171914.GA8622@mail.shareable.org> <20051013101347.GN5856@shell0.pdx.osdl.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: Jamie Lokier , viro@ZenIV.linux.org.uk, nickpiggin@yahoo.com.au, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, akpm@osdl.org Return-path: To: Chris Wright In-Reply-To: <20051013101347.GN5856@shell0.pdx.osdl.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Chris Wright wrote: > * Jamie Lokier (jamie@shareable.org) wrote: > >>Janak Desai wrote: >> >>> Don't allow sighand unsharing if not unsharing vm >> >>Why not? It's permitted to clone with unshared sighand and shared vm, >>and it's useful too. > > > I think that one's just backwards. Although I do question how useful it > is to unshare sighand. Sharing vm is pretty intimate ;-) > > >>It's the combination shared sighand + unshared vm which is not >>allowed by clone - so I think that's what you should refuse. >> >> >>> Don't allow vm unsharing if task cloned with CLONE_THREAD >> >>It would be better to do what clone does, and say "don't allow sighand >>unsharing if task cloned with CLONE_THREAD". This is because >>CLONE_THREAD tasks must have shared signals. > > > Yes, I agree. > > >>In combination with the rule above for sighand (my rule, not yours), >>that implies "don't allow vm unsharing.." as a consequence. >> >> >>> Don't allow vm unsharing if the task is performing async io >> >>Why not? >> >>Async ios are tied to an mm (see lookup_ioctx in fs/aio.c), which may >>be shared among tasks. I see no reason why the async ios can't >>continue and be waited in on in other tasks that may be using the old mm. > > > My concern was the case where there are no other tasks. But I don't > think that's an issue other than having the aio effect of setting up > aio then exiting. > > thanks, > -chris > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > > Thanks Chris and Jamie. I understand the issues that you raised and agree with your change recommendations. I will make the necessary changes, test aio and unsharing of signal handlers (while keeping shared vm) and post the updated patch by tomorrow. -Janak