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Subject: Re: [PATCH] of: Don't allow __of_attached_node_sysfs() without
 CONFIG_SYSFS
To:     Marc Zyngier <maz@kernel.org>, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org
Cc:     robh+dt@kernel.org, kernel-team@android.com
References: <20210820144722.169226-1-maz@kernel.org>
From:   Frank Rowand <frowand.list@gmail.com>
Message-ID: <a67743f9-869b-28df-d714-db15da4ebe06@gmail.com>
Date:   Sun, 22 Aug 2021 23:01:15 -0500
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Hi Marc,

On 8/20/21 9:47 AM, Marc Zyngier wrote:
> Trying to boot without SYSFS, but with OF_DYNAMIC quickly
> results in a crash:
> 
> [    0.088460] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000070
> [...]
> [    0.103927] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.14.0-rc3 #4179
> [    0.105810] Hardware name: linux,dummy-virt (DT)
> [    0.107147] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
> [    0.108876] pc : kernfs_find_and_get_ns+0x3c/0x7c
> [    0.110244] lr : kernfs_find_and_get_ns+0x3c/0x7c
> [...]
> [    0.134087] Call trace:
> [    0.134800]  kernfs_find_and_get_ns+0x3c/0x7c
> [    0.136054]  safe_name+0x4c/0xd0
> [    0.136994]  __of_attach_node_sysfs+0xf8/0x124
> [    0.138287]  of_core_init+0x90/0xfc
> [    0.139296]  driver_init+0x30/0x4c
> [    0.140283]  kernel_init_freeable+0x160/0x1b8
> [    0.141543]  kernel_init+0x30/0x140
> [    0.142561]  ret_from_fork+0x10/0x18
> 
> While not having sysfs isn't a very common option these days,
> it is still expected that such configuration would work.
> 
> Paper over it by bailing out from __of_attach_node_sysfs() if
> CONFIG_SYSFS isn't enabled.

CONFIG_SYSFS should be automatically selected when CONFIG_OF_DYNAMIC
is enabled, and it should not be possible to disable CONFIG_SYSFS
in this case.

Can you send your .config?
What ARCH did you build the kernel with?

Thanks,

Frank


> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  drivers/of/kobj.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/of/kobj.c b/drivers/of/kobj.c
> index a32e60b024b8..6675b5e56960 100644
> --- a/drivers/of/kobj.c
> +++ b/drivers/of/kobj.c
> @@ -119,7 +119,7 @@ int __of_attach_node_sysfs(struct device_node *np)
>  	struct property *pp;
>  	int rc;
>  
> -	if (!of_kset)
> +	if (!IS_ENABLED(CONFIG_SYSFS) || !of_kset)
>  		return 0;
>  
>  	np->kobj.kset = of_kset;
>