On Thu, May 21, 2026 at 11:01:48AM -0700, Nicolin Chen wrote: > FWIW, it was added to address a Sashiko review also: > > By moving the allocation outside the spinlock, the precondition check that > skipped the allocation when the queue was full is bypassed. > > When the queue is full, which can be common during a hardware fault storm > if userspace cannot keep up, the code now unconditionally allocates memory, > copies data, acquires the lock, and then immediately frees the memory and > drops the event. > > Can this tight loop of wasteful slab allocations, memory copies, and > deallocations exacerbate IOMMU fault storms by adding unnecessary CPU > overhead? > > Would it be possible to add an optimistic lockless check, such as > READ_ONCE(veventq->num_events) < veventq->depth, to bypass the allocation > when the queue appears full?
That seems like nonsense to me. > > 6) What do you think about the "but done has > > already been incremented by sizeof(*hdr)" ? unrelated issue? If it > > is simple lets add a patch here to fix it > > I added a patch but didn't include in the series -- Sashiko would > raise more questions against that patch... > > I think it's a separate bug; Sashiko pointed out another in fault > queue as well. Both bugs are at failure (corner cases?) path. > > I'd like to address them separately. Ok Jason
