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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Haoran Wang <haoranwangsec@gmail.com>
Cc: Varun Prakash <varun@chelsio.com>,
	Clark Williams <clrkwllms@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-rt-devel@lists.linux.dev, linux-scsi@vger.kernel.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] libcxgb: use raw_cpu_ptr() in ppm_get_cpu_entries()
Message-ID: <20261019132959.vUxChMBS@linutronix.de>
References: <179241614797.5916.13928836073297916808@whr>
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In-Reply-To: <179241614797.5916.13928836073297916808@whr>

On 2026-10-19 21:22:27 [+0800], Haoran Wang wrote:
> diff --git a/drivers/net/ethernet/chelsio/libcxgb/libcxgb_ppm.c b/drivers/net/ethernet/chelsio/libcxgb/libcxgb_ppm.c
> index 2e3973a32..5f68c5d57 100644
> --- a/drivers/net/ethernet/chelsio/libcxgb/libcxgb_ppm.c
> +++ b/drivers/net/ethernet/chelsio/libcxgb/libcxgb_ppm.c
> @@ -125,10 +125,9 @@ static int ppm_get_cpu_entries(struct cxgbi_ppm *ppm, unsigned int count,
>  	if (!ppm->pool)
>  		return -EINVAL;
>  
> -	cpu = get_cpu();
> -	pool = per_cpu_ptr(ppm->pool, cpu);
> +	cpu = raw_smp_processor_id();
> +	pool = raw_cpu_ptr(ppm->pool);

cpu needs too be obtained after the lock has been acquired.
Please also explain why it is okay to obtain pool belonging to CPU1 on
CPU0.

>  	spin_lock_bh(&pool->lock);
> -	put_cpu();
>  
>  	i = ppm_find_unused_entries(pool->bmap, ppm->pool_index_max,
>  				    pool->next, count, 0);


Sebastian