linux-kernel - Re: [PATCH 5.10 v2] fix csdlock

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Date:   Sat, 7 May 2022 15:00:59 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <rdunlap@...radead.org>
CC:     <peterz@...radead.org>, <gor@...ux.ibm.com>, <tglx@...utronix.de>,
        <axboe@...nel.dk>, <arnd@...db.de>
Subject: Re: [PATCH 5.10 v2] fix csdlock_debug cause arm64 boot panic

ping for review.

On 2022/4/21 15:11, Chen Zhongjin wrote:
> csdlock_debug is a early_param to enable csd_lock_wait
> feature.
> 
> It uses static_branch_enable in early_param which triggers
> a panic on arm64 with config:
> CONFIG_SPARSEMEM=y
> CONFIG_SPARSEMEM_VMEMMAP=n
> 
> The log shows:
> Unable to handle kernel NULL pointer dereference at
> virtual address ", '0' <repeats 16 times>, "
> ...
> Call trace:
> __aarch64_insn_write+0x9c/0x18c
> ...
> static_key_enable+0x1c/0x30
> csdlock_debug+0x4c/0x78
> do_early_param+0x9c/0xcc
> parse_args+0x26c/0x3a8
> parse_early_options+0x34/0x40
> parse_early_param+0x80/0xa4
> setup_arch+0x150/0x6c8
> start_kernel+0x8c/0x720
> ...
> Kernel panic - not syncing: Oops: Fatal exception
> 
> Call trace inside __aarch64_insn_write:
> __nr_to_section
> __pfn_to_page
> phys_to_page
> patch_map
> __aarch64_insn_write
> 
> Here, with CONFIG_SPARSEMEM_VMEMMAP=n, __nr_to_section returns
> NULL and makes the NULL dereference because mem_section is
> initialized in sparse_init after parse_early_param stage.
> 
> So, static_branch_enable shouldn't be used inside early_param.
> To avoid this, I changed it to __setup and fixed this.
> 
> Reported-by: Chen jingwen <chenjingwen6@...wei.com>
> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
> ---
> 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);