| Message ID | 20230713-vfs-eventfd-signal-v1-2-7fda6c5d212b@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | eventfd: simplify signal helpers | expand |
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().
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.
diff --git a/drivers/gpu/drm/i915/gvt/interrupt.c b/drivers/gpu/drm/i915/gvt/interrupt.c index 3d9e09c2add4..31aff6f733d4 100644 --- a/drivers/gpu/drm/i915/gvt/interrupt.c +++ b/drivers/gpu/drm/i915/gvt/interrupt.c @@ -435,7 +435,7 @@ static int inject_virtual_interrupt(struct intel_vgpu *vgpu) */ if (!test_bit(INTEL_VGPU_STATUS_ATTACHED, vgpu->status)) return -ESRCH; - if (vgpu->msi_trigger && eventfd_signal(vgpu->msi_trigger) != 1) + if (vgpu->msi_trigger && !eventfd_signal(vgpu->msi_trigger)) return -EFAULT; return 0; } 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; } /** @@ -82,9 +83,9 @@ __u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, __poll_t mask) * * Returns the amount by which the counter was incremented. */ -__u64 eventfd_signal(struct eventfd_ctx *ctx) +bool eventfd_signal(struct eventfd_ctx *ctx) { - return eventfd_signal_mask(ctx, 1, 0); + return eventfd_signal_mask(ctx, 0); } EXPORT_SYMBOL_GPL(eventfd_signal); diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h index 562089431551..0155ee25f7c8 100644 --- a/include/linux/eventfd.h +++ b/include/linux/eventfd.h @@ -35,8 +35,8 @@ void eventfd_ctx_put(struct eventfd_ctx *ctx); struct file *eventfd_fget(int fd); struct eventfd_ctx *eventfd_ctx_fdget(int fd); struct eventfd_ctx *eventfd_ctx_fileget(struct file *file); -__u64 eventfd_signal(struct eventfd_ctx *ctx); -__u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, __poll_t mask); +bool eventfd_signal(struct eventfd_ctx *ctx); +bool eventfd_signal_mask(struct eventfd_ctx *ctx, __poll_t mask); int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *wait, __u64 *cnt); void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt); @@ -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; } diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index e8096d502a7c..a9359ef73935 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -537,7 +537,7 @@ static void io_eventfd_ops(struct rcu_head *rcu) int ops = atomic_xchg(&ev_fd->ops, 0); if (ops & BIT(IO_EVENTFD_OP_SIGNAL_BIT)) - eventfd_signal_mask(ev_fd->cq_ev_fd, 1, EPOLL_URING_WAKE); + eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE); /* IO_EVENTFD_OP_FREE_BIT may not be set here depending on callback * ordering in a race but if references are 0 we know we have to free @@ -573,7 +573,7 @@ static void io_eventfd_signal(struct io_ring_ctx *ctx) goto out; if (likely(eventfd_signal_allowed())) { - eventfd_signal_mask(ev_fd->cq_ev_fd, 1, EPOLL_URING_WAKE); + eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE); } else { atomic_inc(&ev_fd->refs); if (!atomic_fetch_or(BIT(IO_EVENTFD_OP_SIGNAL_BIT), &ev_fd->ops))
The eventfd_signal_mask() helper was introduced for io_uring and similar to eventfd_signal() it always passed 1 for @n. So don't bother with that argument at all. Signed-off-by: Christian Brauner <brauner@kernel.org> --- drivers/gpu/drm/i915/gvt/interrupt.c | 2 +- fs/eventfd.c | 9 +++++---- include/linux/eventfd.h | 9 ++++----- io_uring/io_uring.c | 4 ++-- 4 files changed, 12 insertions(+), 12 deletions(-)