On 3/28/19 4:24 PM, Jerome Glisse wrote: > 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() ? > That's definitely better, but I want to vote for just doing a check, not taking any locks. I'm not super concerned about the exact name, but I really want a routine that just checks (and optionally asserts, via WARN or BUG), and that's *all*. Then drivers can scatter that around like pixie dust as they see fit. Maybe right before taking a lock, maybe in other places. Decoupled from locking. thanks, -- John Hubbard NVIDIA
