diff mbox series

[2/2] eventfd: simplify eventfd_signal_mask()

Message ID 20230713-vfs-eventfd-signal-v1-2-7fda6c5d212b@kernel.org
State New
Headers show
Series eventfd: simplify signal helpers | expand

Commit Message

Christian Brauner July 13, 2023, 10:05 a.m. UTC
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(-)

Comments

Sean Christopherson July 13, 2023, 2:33 p.m. UTC | #1
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().
diff mbox series

Patch

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))