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 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. 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().