Subject: Re: [PATCH] powerpc: fix unbalanced node refcount in check_kvm_guest()

From: Srikar Dronamraju <[email-masked]>
Date: Wed, 29 Sep 2021 12:59:25 +0530

* Nathan Lynch <[email-masked]> [2021-09-28 07:45:50]:

> When check_kvm_guest() succeeds in looking up a /hypervisor OF node, it
> returns without performing a matching put for the lookup, leaving the
> node's reference count elevated.
> 
> Add the necessary call to of_node_put(), rearranging the code slightly to
> avoid repetition or goto.
> 

Looks good to me.

I do see few other cases where we call of_find_node calls without
of_node_put().

Some of them that I saw were in

find_legacy_serial_ports()  in  arch/powerpc/kernel/legacy_serial.c
proc_ppc64_create in arch/powerpc/proc/powerpc.c
update_events_in_group in arch/powerpc/perf/imc-pmu.c
cell_iommu_init_disabled in arch/powerpc/platforms/cell/iommu.c
cell_publish_devices in arch/powerpc/platforms/cell/setup.c
spufs_init_isolated_loader in arch/powerpc/platforms/cell/spufs/inode.c
holly_init_pci / holly_restart and holly_init_IRQ in arch/powerpc/platforms/embedded6xx/holly.c

Reviewed-by: Srikar Dronamraju <[email-masked]>

> Signed-off-by: Nathan Lynch <[email-masked]>
> Fixes: 107c55005fbd ("powerpc/pseries: Add KVM guest doorbell restrictions")
> ---
>  arch/powerpc/kernel/firmware.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/firmware.c b/arch/powerpc/kernel/firmware.c
> index c7022c41cc31..20328f72f9f2 100644
> --- a/arch/powerpc/kernel/firmware.c
> +++ b/arch/powerpc/kernel/firmware.c
> @@ -31,11 +31,10 @@ int __init check_kvm_guest(void)
>  	if (!hyper_node)
>  		return 0;
> 
> -	if (!of_device_is_compatible(hyper_node, "linux,kvm"))
> -		return 0;
> -
> -	static_branch_enable(&kvm_guest);
> +	if (of_device_is_compatible(hyper_node, "linux,kvm"))
> +		static_branch_enable(&kvm_guest);
> 
> +	of_node_put(hyper_node);
>  	return 0;
>  }
>  core_initcall(check_kvm_guest); // before kvm_guest_init()
> -- 
> 2.31.1
> 

-- 
Thanks and Regards
Srikar Dronamraju