linux-kernel - Re: [PATCH] riscv: Prevent a bad reference count on CPU nodes

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Message-ID: <ZvrRmqvmVjvmACsd@sunil-laptop>
Date: Mon, 30 Sep 2024 21:58:10 +0530
From: Sunil V L <sunilvl@...tanamicro.com>
To: Miquel Sabaté Solà <mikisabate@...il.com>
Cc: paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
	cuiyunhui@...edance.com, sudeep.holla@....com,
	jeremy.linton@....com, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Prevent a bad reference count on CPU nodes

On Fri, Sep 13, 2024 at 10:00:52AM +0200, Miquel Sabaté Solà wrote:
> When populating cache leaves we previously fetched the CPU device node
> at the very beginning. But when ACPI is enabled we go through a
> specific branch which returns early and does not call 'of_node_put' for
> the node that was acquired.
> 
> Since we are not using a CPU device node for the ACPI code anyways, we
> can simply move the initialization of it just passed the ACPI block, and
> we are guaranteed to have an 'of_node_put' call for the acquired node.
> This prevents a bad reference count of the CPU device node.
> 
> Moreover, the previous function did not check for errors when acquiring
> the device node, so a return -ENOENT has been added for that case.
> 
> Signed-off-by: Miquel Sabaté Solà <mikisabate@...il.com>
> ---
> I was wondering if this should also be sent to stable, but  I have not seen
> a report on it, and this is not responsible for an oops or anything like that.
> So in the end I decided not to, but maybe you consider otherwise.
> 
>  arch/riscv/kernel/cacheinfo.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/kernel/cacheinfo.c b/arch/riscv/kernel/cacheinfo.c
> index d6c108c50cba..d32dfdba083e 100644
> --- a/arch/riscv/kernel/cacheinfo.c
> +++ b/arch/riscv/kernel/cacheinfo.c
> @@ -75,8 +75,7 @@ int populate_cache_leaves(unsigned int cpu)
>  {
>  	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
>  	struct cacheinfo *this_leaf = this_cpu_ci->info_list;
> -	struct device_node *np = of_cpu_device_node_get(cpu);
> -	struct device_node *prev = NULL;
> +	struct device_node *np, *prev;
>  	int levels = 1, level = 1;
> 
>  	if (!acpi_disabled) {
> @@ -100,6 +99,10 @@ int populate_cache_leaves(unsigned int cpu)
>  		return 0;
>  	}
> 
> +	np = of_cpu_device_node_get(cpu);
> +	if (!np)
> +		return -ENOENT;
> +
LGTM.

Reviewed-by: Sunil V L <sunilvl@...tanamicro.com>

Thanks,
Sunil