mshv: clear eventfd counter on irqfd shutdown

[PATCH] mshv: clear eventfd counter on irqfd shutdown

Posted by Carlos López 2 weeks, 2 days ago

While unhooking from the irqfd waitqueue, clear the internal eventfd
counter by using eventfd_ctx_remove_wait_queue() instead of
remove_wait_queue(), preventing potential spurious interrupts. This
removes the need to store a pointer into the workqueue, as the eventfd
already keeps track of it.

This mimicks what other similar subsystems do on their equivalent paths
with their irqfds (KVM, Xen, ACRN support, etc).

Signed-off-by: Carlos López <clopez@suse.de>
---
 drivers/hv/mshv_eventfd.c | 5 ++---
 drivers/hv/mshv_eventfd.h | 1 -
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/hv/mshv_eventfd.c b/drivers/hv/mshv_eventfd.c
index d93a18f09c76..4432063e963d 100644
--- a/drivers/hv/mshv_eventfd.c
+++ b/drivers/hv/mshv_eventfd.c
@@ -247,12 +247,13 @@ static void mshv_irqfd_shutdown(struct work_struct *work)
 {
 	struct mshv_irqfd *irqfd =
 			container_of(work, struct mshv_irqfd, irqfd_shutdown);
+	u64 cnt;
 
 	/*
 	 * Synchronize with the wait-queue and unhook ourselves to prevent
 	 * further events.
 	 */
-	remove_wait_queue(irqfd->irqfd_wqh, &irqfd->irqfd_wait);
+	eventfd_ctx_remove_wait_queue(irqfd->irqfd_eventfd_ctx, &irqfd->irqfd_wait, &cnt);
 
 	if (irqfd->irqfd_resampler) {
 		mshv_irqfd_resampler_shutdown(irqfd);
@@ -371,8 +372,6 @@ static void mshv_irqfd_queue_proc(struct file *file, wait_queue_head_t *wqh,
 	struct mshv_irqfd *irqfd =
 			container_of(polltbl, struct mshv_irqfd, irqfd_polltbl);
 
-	irqfd->irqfd_wqh = wqh;
-
 	/*
 	 * TODO: Ensure there isn't already an exclusive, priority waiter, e.g.
 	 * that the irqfd isn't already bound to another partition.  Only the
diff --git a/drivers/hv/mshv_eventfd.h b/drivers/hv/mshv_eventfd.h
index 332e7670a344..464c6b81ab33 100644
--- a/drivers/hv/mshv_eventfd.h
+++ b/drivers/hv/mshv_eventfd.h
@@ -32,7 +32,6 @@ struct mshv_irqfd {
 	struct mshv_lapic_irq		     irqfd_lapic_irq;
 	struct hlist_node		     irqfd_hnode;
 	poll_table			     irqfd_polltbl;
-	wait_queue_head_t		    *irqfd_wqh;
 	wait_queue_entry_t		     irqfd_wait;
 	struct work_struct		     irqfd_shutdown;
 	struct mshv_irqfd_resampler	    *irqfd_resampler;

base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
-- 
2.51.0

Re: [PATCH] mshv: clear eventfd counter on irqfd shutdown

Posted by Wei Liu 3 days, 13 hours ago

On Thu, Jan 22, 2026 at 12:41:31PM +0100, Carlos López wrote:
> While unhooking from the irqfd waitqueue, clear the internal eventfd
> counter by using eventfd_ctx_remove_wait_queue() instead of
> remove_wait_queue(), preventing potential spurious interrupts. This
> removes the need to store a pointer into the workqueue, as the eventfd
> already keeps track of it.
> 
> This mimicks what other similar subsystems do on their equivalent paths
> with their irqfds (KVM, Xen, ACRN support, etc).
> 
> Signed-off-by: Carlos López <clopez@suse.de>

This looks like a good change to me. I've queued it to hyperv-next.
Thanks!

Also CC our kernel folks just in case I missed something.

Wei

> ---
>  drivers/hv/mshv_eventfd.c | 5 ++---
>  drivers/hv/mshv_eventfd.h | 1 -
>  2 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hv/mshv_eventfd.c b/drivers/hv/mshv_eventfd.c
> index d93a18f09c76..4432063e963d 100644
> --- a/drivers/hv/mshv_eventfd.c
> +++ b/drivers/hv/mshv_eventfd.c
> @@ -247,12 +247,13 @@ static void mshv_irqfd_shutdown(struct work_struct *work)
>  {
>  	struct mshv_irqfd *irqfd =
>  			container_of(work, struct mshv_irqfd, irqfd_shutdown);
> +	u64 cnt;
>  
>  	/*
>  	 * Synchronize with the wait-queue and unhook ourselves to prevent
>  	 * further events.
>  	 */
> -	remove_wait_queue(irqfd->irqfd_wqh, &irqfd->irqfd_wait);
> +	eventfd_ctx_remove_wait_queue(irqfd->irqfd_eventfd_ctx, &irqfd->irqfd_wait, &cnt);
>  
>  	if (irqfd->irqfd_resampler) {
>  		mshv_irqfd_resampler_shutdown(irqfd);
> @@ -371,8 +372,6 @@ static void mshv_irqfd_queue_proc(struct file *file, wait_queue_head_t *wqh,
>  	struct mshv_irqfd *irqfd =
>  			container_of(polltbl, struct mshv_irqfd, irqfd_polltbl);
>  
> -	irqfd->irqfd_wqh = wqh;
> -
>  	/*
>  	 * TODO: Ensure there isn't already an exclusive, priority waiter, e.g.
>  	 * that the irqfd isn't already bound to another partition.  Only the
> diff --git a/drivers/hv/mshv_eventfd.h b/drivers/hv/mshv_eventfd.h
> index 332e7670a344..464c6b81ab33 100644
> --- a/drivers/hv/mshv_eventfd.h
> +++ b/drivers/hv/mshv_eventfd.h
> @@ -32,7 +32,6 @@ struct mshv_irqfd {
>  	struct mshv_lapic_irq		     irqfd_lapic_irq;
>  	struct hlist_node		     irqfd_hnode;
>  	poll_table			     irqfd_polltbl;
> -	wait_queue_head_t		    *irqfd_wqh;
>  	wait_queue_entry_t		     irqfd_wait;
>  	struct work_struct		     irqfd_shutdown;
>  	struct mshv_irqfd_resampler	    *irqfd_resampler;
> 
> base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
> -- 
> 2.51.0
>