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 struct mmu_notifier_range (ie the args to invalidate_range) -> range 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 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? Jason _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
