On Thu, Mar 28, 2019 at 04:20:37PM -0700, John Hubbard wrote: > On 3/28/19 4:05 PM, Jerome Glisse wrote: > > On Thu, Mar 28, 2019 at 03:43:33PM -0700, John Hubbard wrote: > >> On 3/28/19 3:40 PM, Jerome Glisse wrote: > >>> On Thu, Mar 28, 2019 at 03:25:39PM -0700, John Hubbard wrote: > >>>> On 3/28/19 3:08 PM, Jerome Glisse wrote: > >>>>> On Thu, Mar 28, 2019 at 02:41:02PM -0700, John Hubbard wrote: > >>>>>> On 3/28/19 2:30 PM, Jerome Glisse wrote: > >>>>>>> On Thu, Mar 28, 2019 at 01:54:01PM -0700, John Hubbard wrote: > >>>>>>>> On 3/25/19 7:40 AM, jglisse@xxxxxxxxxx wrote: > >>>>>>>>> From: Jérôme Glisse <jglisse@xxxxxxxxxx> > >>>> [...] > >>>> OK, so let's either drop this patch, or if merge windows won't allow that, > >>>> then *eventually* drop this patch. And instead, put in a hmm_sanity_check() > >>>> that does the same checks. > >>> > >>> RDMA depends on this, so does the nouveau patchset that convert to new API. > >>> So i do not see reason to drop this. They are user for this they are posted > >>> and i hope i explained properly the benefit. > >>> > >>> It is a common pattern. Yes it only save couple lines of code but down the > >>> road i will also help for people working on the mmap_sem patchset. > >>> > >> > >> It *adds* a couple of lines that are misleading, because they look like they > >> make things safer, but they don't actually do so. > > > > It is not about safety, sorry if it confused you but there is nothing about > > safety here, i can add a big fat comment that explains that there is no safety > > here. The intention is to allow the page fault handler that potential have > > hundred of page fault queue up to abort as soon as it sees that it is pointless > > to keep faulting on a dying process. > > > > Again if we race it is _fine_ nothing bad will happen, we are just doing use- > > less work that gonna be thrown on the floor and we are just slowing down the > > process tear down. > > > > In addition to a comment, how about naming this thing to indicate the above > intention? I have a really hard time with this odd down_read() wrapper, which > allows code to proceed without really getting a lock. It's just too wrong-looking. > If it were instead named: > > hmm_is_exiting() What about: hmm_lock_mmap_if_alive() ? > > and had a comment about why racy is OK, then I'd be a lot happier. :) Will add fat comment. Cheers, Jérôme
