linux-kernel - Re: [PATCH 1/1] mshv: Fix compiler warning about cast converting incompatible function type

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Message-ID: <e99513ac-a790-424b-9b80-4a91fd87cba2@linux.microsoft.com>
Date: Mon, 19 Jan 2026 11:02:01 +0530
From: Naman Jain <namjain@...ux.microsoft.com>
To: mhklinux@...look.com, kys@...rosoft.com, haiyangz@...rosoft.com,
 wei.liu@...nel.org, decui@...rosoft.com, longli@...rosoft.com,
 linux-hyperv@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mshv: Fix compiler warning about cast converting
 incompatible function type



On 1/18/2026 10:32 PM, mhkelley58@...il.com wrote:
> From: Michael Kelley <mhklinux@...look.com>
> 
> In mshv_vtl_sint_ioctl_pause_msg_stream(), the reference to function
> mshv_vtl_synic_mask_vmbus_sint() is cast to type smp_call_func_t. The
> cast generates a compiler warning because the function signature of
> mshv_vtl_synic_mask_vmbus_sint() doesn't match smp_call_func_t.
> 
> There's no actual bug here because the mis-matched function signatures
> are compatible at runtime. Nonetheless, eliminate the compiler warning
> by changing the function signature of mshv_vtl_synic_mask_vmbus_sint()
> to match what on_each_cpu() expects. Remove the cast because it is then
> no longer necessary.
> 
> No functional change.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202601170352.qbh3EKH5-lkp@intel.com/
> Signed-off-by: Michael Kelley <mhklinux@...look.com>
> ---
>   drivers/hv/mshv_vtl_main.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c
> index 2cebe9de5a5a..7bbbce009732 100644
> --- a/drivers/hv/mshv_vtl_main.c
> +++ b/drivers/hv/mshv_vtl_main.c
> @@ -845,9 +845,10 @@ static const struct file_operations mshv_vtl_fops = {
>   	.mmap = mshv_vtl_mmap,
>   };
>   
> -static void mshv_vtl_synic_mask_vmbus_sint(const u8 *mask)
> +static void mshv_vtl_synic_mask_vmbus_sint(void *info)
>   {
>   	union hv_synic_sint sint;
> +	const u8 *mask = info;
>   
>   	sint.as_uint64 = 0;
>   	sint.vector = HYPERVISOR_CALLBACK_VECTOR;
> @@ -999,7 +1000,7 @@ static int mshv_vtl_sint_ioctl_pause_msg_stream(struct mshv_sint_mask __user *ar
>   	if (copy_from_user(&mask, arg, sizeof(mask)))
>   		return -EFAULT;
>   	guard(mutex)(&vtl2_vmbus_sint_mask_mutex);
> -	on_each_cpu((smp_call_func_t)mshv_vtl_synic_mask_vmbus_sint, &mask.mask, 1);
> +	on_each_cpu(mshv_vtl_synic_mask_vmbus_sint, &mask.mask, 1);
>   	WRITE_ONCE(vtl_synic_mask_vmbus_sint_masked, mask.mask != 0);
>   	if (mask.mask)
>   		wake_up_interruptible_poll(&fd_wait_queue, EPOLLIN);

Thank you Michael for fixing this.

Reviewed-by: Naman Jain <namjain@...ux.microsoft.com>