From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerome Glisse Subject: Re: [PATCH 1/6] mmput: use notifier chain to call subsystem exit handler. Date: Tue, 1 Jul 2014 17:32:09 -0400 Message-ID: <20140701213208.GC3322@gmail.com> References: <019CCE693E457142B37B791721487FD91806B836@storexdag01.amd.com> <20140630154042.GD26537@8bytes.org> <20140630160604.GF1956@gmail.com> <20140630181623.GE26537@8bytes.org> <20140630183556.GB3280@gmail.com> <20140701091535.GF26537@8bytes.org> <019CCE693E457142B37B791721487FD91806DD8B@storexdag01.amd.com> <20140701110018.GH26537@8bytes.org> <20140701193343.GB3322@gmail.com> <20140701210620.GL26537@8bytes.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: <20140701210620.GL26537@8bytes.org> Sender: owner-linux-mm@kvack.org To: Joerg Roedel Cc: "Gabbay, Oded" , "Deucher, Alexander" , "Lewycky, Andrew" , "Cornwall, Jay" , "Bridgman, John" , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "mgorman@suse.de" , "hpa@zytor.com" , "peterz@infraread.org" , "aarcange@redhat.com" , "riel@redhat.com" , "jweiner@redhat.com" , "torvalds@linux-foundation.org" , Mark Hairgrove , Jatin Kumar , Subhash Gutti , Lucien Dunning , Cameron Buschardt , Ar List-Id: iommu@lists.linux-foundation.org On Tue, Jul 01, 2014 at 11:06:20PM +0200, Joerg Roedel wrote: > On Tue, Jul 01, 2014 at 03:33:44PM -0400, Jerome Glisse wrote: > > On Tue, Jul 01, 2014 at 01:00:18PM +0200, Joerg Roedel wrote: > > > No, its not in this case. The file descriptor is used to connect a > > > process address space with a device context. Thus without the mappi= ngs > > > the file-descriptor is useless and the mappings should stay in-tact > > > until the fd is closed. > > >=20 > > > It would be a very bad semantic for userspace if a fd that is passe= d on > > > fails on the other side because the sending process died. > >=20 > > Consider use case where there is no file associated with the mmu_noti= fier > > ie there is no device file descriptor that could hold and take care o= f > > mmu_notifier destruction and cleanup. We need this call chain for thi= s > > case. >=20 > Example of such a use-case where no fd will be associated? >=20 > Anyway, even without an fd, there will always be something that sets th= e > mm->device binding up (calling mmu_notifier_register) and tears it down > in the end (calling mmu_notifier_unregister). And this will be the > places where any resources left from the .release call-back can be > cleaned up. >=20 That's the whole point we can not do what we want without the callback ie the place where we do the cleanup is the mm callback we need. If you do n= ot like the call chain than we will just add ourself as another caller in th= e exact same spot where the notifier chain is which Andrew disliked because there are already enough submodule that are interested in being inform of mm destruction. Cheers, J=E9r=F4me -- 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