On Thu, Jul 13, 2023 at 07:33:05AM -0700, Sean Christopherson wrote: > On Thu, Jul 13, 2023, Christian Brauner wrote: > > diff --git a/fs/eventfd.c b/fs/eventfd.c > > index dc9e01053235..077be5da72bd 100644 > > --- a/fs/eventfd.c > > +++ b/fs/eventfd.c > > @@ -43,9 +43,10 @@ struct eventfd_ctx { > > int id; > > }; > > > > -__u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, __poll_t mask) > > +bool eventfd_signal_mask(struct eventfd_ctx *ctx, __poll_t mask) > > { > > unsigned long flags; > > + __u64 n = 1; > > > > /* > > * Deadlock or stack overflow issues can happen if we recurse here > > @@ -68,7 +69,7 @@ __u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 > > n, __poll_t mask) > > current->in_eventfd = 0; > > spin_unlock_irqrestore(&ctx->wqh.lock, flags); > > > > - return n; > > + return n == 1; > > } > > ... > > > @@ -58,13 +58,12 @@ static inline struct eventfd_ctx *eventfd_ctx_fdget(int > > fd) > > return ERR_PTR(-ENOSYS); > > } > > > > -static inline int eventfd_signal(struct eventfd_ctx *ctx) > > +static inline bool eventfd_signal(struct eventfd_ctx *ctx) > > { > > return -ENOSYS; > > } > > > > -static inline int eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, > > - unsigned mask) > > +static inline bool eventfd_signal_mask(struct eventfd_ctx *ctx, unsigned > > mask) > > { > > return -ENOSYS; > > This will morph to "true" for what should be an error case. One option would > be
Ewww, that means it did return -ENOSYS before any of this. > to have eventfd_signal_mask() return 0/-errno instead of the count, but > looking > at all the callers, nothing ever actually consumes the result. > > KVMGT morphs failure into -EFAULT > > if (vgpu->msi_trigger && eventfd_signal(vgpu->msi_trigger, 1) != 1) > return -EFAULT; > > but the only caller of that user ignores the return value. > > if (vgpu_vreg(vgpu, i915_mmio_reg_offset(GEN8_MASTER_IRQ)) > & ~GEN8_MASTER_IRQ_CONTROL) > inject_virtual_interrupt(vgpu); > > The sample driver in samples/vfio-mdev/mtty.c uses a similar pattern: prints > an > error but otherwise ignores the result. > > So why not return nothing? That will simplify eventfd_signal_mask() a wee bit > more, and eliminate that bizarre return value confusion for the ugly stubs, > e.g. Yeah, it used to return an int in the non-eventfd and a __u64 in the eventfd case. > > void eventfd_signal_mask(struct eventfd_ctx *ctx, unsigned mask) > { > unsigned long flags; > > /* > * Deadlock or stack overflow issues can happen if we recurse here > * through waitqueue wakeup handlers. If the caller users potentially > * nested waitqueues with custom wakeup handlers, then it should > * check eventfd_signal_allowed() before calling this function. If > * it returns false, the eventfd_signal() call should be deferred to a > * safe context. > */ > if (WARN_ON_ONCE(current->in_eventfd)) > return; > > spin_lock_irqsave(&ctx->wqh.lock, flags); > current->in_eventfd = 1; > if (ctx->count < ULLONG_MAX) > ctx->count++; > if (waitqueue_active(&ctx->wqh)) > wake_up_locked_poll(&ctx->wqh, EPOLLIN | mask); > current->in_eventfd = 0; > spin_unlock_irqrestore(&ctx->wqh.lock, flags); > } > > You could even go further and unify the real and stub versions of > eventfd_signal(). The reason I didn't make eventfd_signal_mask() return void was that it was called from eventfd_signal() which did, I didn't realize the caller didn't actually consume the return value. If we can let both return void it gets simpler. Thanks for that.