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Subject: Re: [PATCH] of: fix phandle cache creation for DTs with no phandles
To:     Rob Herring <robh@kernel.org>,
        Finn Thain <fthain@telegraphics.com.au>,
        Stan Johnson <userm57@yahoo.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc:     devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, stable@vger.kernel.org
References: <20180911145607.6009-1-robh@kernel.org>
From:   Frank Rowand <frowand.list@gmail.com>
Message-ID: <0ecd44b5-3faa-6b30-d47f-dd06efbcadd6@gmail.com>
Date:   Tue, 11 Sep 2018 09:02:43 -0700
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On 09/11/18 07:56, Rob Herring wrote:
> With commit 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of
> of_find_node_by_phandle()"), a G3 PowerMac fails to boot. The root cause
> is the DT for this system has no phandle properties when booted with
> BootX. of_populate_phandle_cache() does not handle the case of no
> phandles correctly. The problem is roundup_pow_of_two() for 0 is
> undefined. The implementation subtracts 1 underflowing and then things
> are in the weeds.
> 
> Fixes: 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")
> Cc: stable@vger.kernel.org # 4.17+
> Reported-by: Finn Thain <fthain@telegraphics.com.au>
> Tested-by: Stan Johnson <userm57@yahoo.com>
> Cc: Frank Rowand <frowand.list@gmail.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Rob Herring <robh@kernel.org>
> ---
> Here's a formal patch of what Stan tested. Will send to Linus this week.
> 
> Rob
> 
>  drivers/of/base.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index a055cd1ef96d..17ae594b7014 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -140,6 +140,9 @@ void of_populate_phandle_cache(void)
>  		if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL)
>  			phandles++;
>  
> +	if (!phandles)
> +		goto out;
> +
>  	cache_entries = roundup_pow_of_two(phandles);
>  	phandle_cache_mask = cache_entries - 1;
>  
> 


Reviewed-by: Frank Rowand <frank.rowand@sony.com>