linux-kernel - Re: [PATCH] mach-mvebu: coherency: Judgment after pointer p increases allocation

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Message-ID: <Y3wVmPQFVesgmpxN@lunn.ch>
Date:   Tue, 22 Nov 2022 01:19:36 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Li zeming <zeming@...china.com>
Cc:     gregory.clement@...tlin.com, sebastian.hesselbarth@...il.com,
        linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mach-mvebu: coherency: Judgment after pointer p
 increases allocation

On Mon, Nov 21, 2022 at 06:01:22PM +0800, Li zeming wrote:
> Add judgment statements at the position after pointer p allocates memory
> to avoid the abnormal impact of low probability allocation failure.
> 
> Signed-off-by: Li zeming <zeming@...china.com>
> ---
>  arch/arm/mach-mvebu/coherency.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c
> index a6b621ff0b87..2bc69dd059d6 100644
> --- a/arch/arm/mach-mvebu/coherency.c
> +++ b/arch/arm/mach-mvebu/coherency.c
> @@ -191,8 +191,10 @@ static void __init armada_375_380_coherency_init(struct device_node *np)
>  		struct property *p;
>  
>  		p = kzalloc(sizeof(*p), GFP_KERNEL);
> -		p->name = kstrdup("arm,io-coherent", GFP_KERNEL);
> -		of_add_property(cache_dn, p);
> +		if (p) {
> +			p->name = kstrdup("arm,io-coherent", GFP_KERNEL);
> +			of_add_property(cache_dn, p);
> +		}

The comment before this says:
	/*
	 * Add the PL310 property "arm,io-coherent". This makes sure the
	 * outer sync operation is not used, which allows to
	 * workaround the system erratum that causes deadlocks when
	 * doing PCIe in an SMP situation on Armada 375 and Armada
	 * 38x.
	 */

Skipping adding the property because we are out of memory is probably
not a good idea, it is going to cause very hard to find deadlocks.
Actually being out of memory so early in the boot indicates something
very bad is going on anyway. So i think dereferencing the NULL pointer
is the least of our worries.

If you really want to do some sort of check here, BUG_ON(!p);

   Andrew