linux-kernel - Re: [PATCH v4] locking/csd_lock: change csdlock_debug from early_param to _

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Date:   Tue, 17 May 2022 11:22:04 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-arch@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
        <stable@...r.kernel.org>
CC:     <peterz@...radead.org>, <tglx@...utronix.de>, <namit@...are.com>,
        <gor@...ux.ibm.com>, <rdunlap@...radead.org>, <paulmck@...nel.org>,
        <mingo@...nel.org>, <jgross@...e.com>,
        <gregkh@...uxfoundation.org>, <mpe@...erman.id.au>
Subject: Re: [PATCH v4] locking/csd_lock: change csdlock_debug from
 early_param to __setup

On 2022/5/10 17:46, Chen Zhongjin wrote:
> csdlock_debug uses early_param and static_branch_enable() to enable
> csd_lock_wait feature, which triggers a panic on arm64 with config:
> CONFIG_SPARSEMEM=y
> CONFIG_SPARSEMEM_VMEMMAP=n
> 
> With CONFIG_SPARSEMEM_VMEMMAP=n, __nr_to_section is called in
> static_key_enable() and returns NULL which makes NULL dereference
> because mem_section is initialized in sparse_init() which is later
> than parse_early_param() stage.
> 
> For powerpc this is also broken, because early_param stage is
> earlier than jump_label_init() so static_key_enable won't work.
> powerpc throws an warning: "static key 'xxx' used before call
> to jump_label_init()".
> 
> Thus, early_param is too early for csd_lock_wait to run
> static_branch_enable(), so changes it to __setup to fix these.
> 
> Fixes: 8d0968cc6b8f ("locking/csd_lock: Add boot parameter for controlling CSD lock debugging")
> Cc: stable@...r.kernel.org
> Reported-by: Chen jingwen <chenjingwen6@...wei.com>
> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
> ---
> Change v3 -> v4:
> Fix title and description because this fix is also applied
> to powerpc.
> For more detailed arm64 bug report see:
> https://lore.kernel.org/linux-arm-kernel/e8715911-f835-059d-27f8-cc5f5ad30a07@huawei.com/t/
> 
> Change v2 -> v3:
> Add module name in title
> 
> Change v1 -> v2:
> Fix return 1 for __setup
> ---
>  kernel/smp.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 65a630f62363..381eb15cd28f 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -174,9 +174,9 @@ static int __init csdlock_debug(char *str)
>  	if (val)
>  		static_branch_enable(&csdlock_debug_enabled);
>  
> -	return 0;
> +	return 1;
>  }
> -early_param("csdlock_debug", csdlock_debug);
> +__setup("csdlock_debug=", csdlock_debug);
>  
>  static DEFINE_PER_CPU(call_single_data_t *, cur_csd);
>  static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);

Ping for review. Thanks！