linux-kernel - Re: [PATCH v1] erofs: use raw_smp_processor_id() to get buffer from global buffer pool

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Date: Tue, 9 Apr 2024 06:48:41 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Sandeep Dhavale <dhavale@...gle.com>, Gao Xiang <xiang@...nel.org>,
 Chao Yu <chao@...nel.org>, Yue Hu <huyue2@...lpad.com>,
 Jeffle Xu <jefflexu@...ux.alibaba.com>, Chunhai Guo <guochunhai@...o.com>
Cc: linux-erofs@...ts.ozlabs.org,
 syzbot+27cc650ef45b379dfe5a@...kaller.appspotmail.com,
 kernel-team@...roid.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] erofs: use raw_smp_processor_id() to get buffer from
 global buffer pool

Hi Sandeep,

On 2024/4/9 05:52, Sandeep Dhavale wrote:
> erofs will decompress in the preemptible context (kworker or per cpu
> thread). As smp_processor_id() cannot be used in preemptible contexts,
> use raw_smp_processor_id() instead to index into global buffer pool.
> 
> Reported-by: syzbot+27cc650ef45b379dfe5a@...kaller.appspotmail.com
> Fixes: 7a7513292cc6 ("erofs: rename per-CPU buffers to global buffer pool and make it configurable")
> Signed-off-by: Sandeep Dhavale <dhavale@...gle.com>

Thanks for catching this, since the original patch is
for next upstream cycle, may I fold this fix in the
original patch?

I will add your credit into the original patch.

Thanks,
Gao Xiang

> ---
>   fs/erofs/zutil.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/erofs/zutil.c b/fs/erofs/zutil.c
> index b9b99158bb4e..036024bce9f7 100644
> --- a/fs/erofs/zutil.c
> +++ b/fs/erofs/zutil.c
> @@ -30,7 +30,7 @@ static struct shrinker *erofs_shrinker_info;
>   
>   static unsigned int z_erofs_gbuf_id(void)
>   {
> -	return smp_processor_id() % z_erofs_gbuf_count;
> +	return raw_smp_processor_id() % z_erofs_gbuf_count;
>   }
>   
>   void *z_erofs_get_gbuf(unsigned int requiredpages)