On Tue 30-03-21 16:08:36, Muchun Song wrote: > On Tue, Mar 30, 2021 at 4:01 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Mon 29-03-21 16:23:55, Mike Kravetz wrote: > > > Ideally, cma_release could be called from any context. However, that is > > > not possible because a mutex is used to protect the per-area bitmap. > > > Change the bitmap to an irq safe spinlock. > > > > I would phrase the changelog slightly differerent > > " > > cma_release is currently a sleepable operatation because the bitmap > > manipulation is protected by cma->lock mutex. Hugetlb code which relies > > on cma_release for CMA backed (giga) hugetlb pages, however, needs to be > > irq safe. > > > > The lock doesn't protect any sleepable operation so it can be changed to > > a (irq aware) spin lock. The bitmap processing should be quite fast in > > typical case but if cma sizes grow to TB then we will likely need to > > replace the lock by a more optimized bitmap implementation. > > " > > > > it seems that you are overusing irqsave variants even from context which > > are never called from the IRQ context so they do not need storing flags. > > > > [...] > > > @@ -391,8 +391,9 @@ static void cma_debug_show_areas(struct cma *cma) > > > unsigned long start = 0; > > > unsigned long nr_part, nr_total = 0; > > > unsigned long nbits = cma_bitmap_maxno(cma); > > > + unsigned long flags; > > > > > > - mutex_lock(&cma->lock); > > > + spin_lock_irqsave(&cma->lock, flags); > > > > spin_lock_irq should be sufficient. This is only called from the > > allocation context and that is never called from IRQ context. > > This makes me think more. I think that spin_lock should be > sufficient. Right? Nope. Think of the following scenario spin_lock(cma->lock); <IRQ> put_page __free_huge_page cma_release spin_lock_irqsave() DEADLOCK -- Michal Hocko SUSE Labs
