On Tue, Dec 03, 2019 at 02:42:12AM +0000, Jason Gunthorpe wrote: > On Sat, Nov 30, 2019 at 10:23:31AM -0800, Linus Torvalds wrote: > > On Sat, Nov 30, 2019 at 10:03 AM Linus Torvalds > > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > I'll try to figure the code out, but my initial reaction was "yeah, > > > not in my VM". > > > > Why is it ok to sometimes do > > > > WRITE_ONCE(mni->invalidate_seq, cur_seq); > > > > (to pair with the unlocked READ_ONCE), and sometimes then do > > > > mni->invalidate_seq = mmn_mm->invalidate_seq; > > > > My initial guess was that latter is only done at initialization time, > > but at least in one case it's done *after* the mni has been added to > > the mmn_mm (oh, how I despise those names - I can only repeat: WTF?). > > Yes, the only occurrences are in the notifier_insert, under the > spinlock. The one case where it is out of the natural order was to > make the manipulation of seq a bit saner, but in all cases since the > spinlock is held there is no way for another thread to get the pointer > to the 'mmu_interval_notifier *' to do the unlocked read. > > Regarding the ugly names.. Naming has been really hard here because > currently everything is a 'mmu notifier' and the natural abberviations > from there are crummy. Here is the basic summary: > > struct mmu_notifier_mm (ie the mm->mmu_notifier_mm) > -> mmn_mm > struct mm_struct > -> mm > struct mmu_notifier (ie the user subscription to the mm_struct) > -> mn > struct mmu_interval_notifier (the other kind of user subscription) > -> mni What about "interval" the context should already tell people it is related to mmu notifier and thus a notifier. I would just remove the notifier suffix, this would match the below range. > struct mmu_notifier_range (ie the args to invalidate_range) > -> range Yeah range as context should tell you it is related to mmu notifier. > > I can send a patch to switch mmn_mm to mmu_notifier_mm, which is the > only pre-existing name for this value. But IIRC, it is a somewhat ugly > with long line wrapping. 'mni' is a pain, I have to reflect on that. > (honesly, I dislike mmu_notififer_mm quite a lot too) > > I think it would be overall nicer with better names for the original > structs. Perhaps: > > mmn_* - MMU notifier prefix > mmn_state <- struct mmu_notifier_mm > mmn_subscription (mmn_sub) <- struct mmu_notifier > mmn_range_subscription (mmn_range_sub) <- struct mmu_interval_notifier > mmn_invalidate_desc <- struct mmu_notifier_range This looks good. > > At least this is how I describe them in my mind.. This is a lot of > churn, and spreads through many drivers. This is why I kept the names > as-is and we ended up with the also quite bad 'mmu_interval_notifier' > > Maybe just switch mmu_notifier_mm for mmn_state and leave the drivers > alone? > > Anyone on the CC list have advice? Maybe we can do a semantic patch to do convertion and then Linus can easily apply the patch by just re-running the coccinelle. Cheers, Jérôme
