linux-kernel - Re: [PATCH] coresight: etm3x: convert struct etm_drvdata's spinlock to raw

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Date:   Mon, 7 Aug 2023 15:40:34 +0200
From:   Sebastian Siewior <bigeasy@...utronix.de>
To:     quanyang.wang@...driver.com
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tingwei Zhang <tingwei@...eaurora.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Kim Phillips <kim.phillips@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-rt-users@...r.kernel.org, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: etm3x: convert struct etm_drvdata's spinlock
 to raw_spinlock

On 2023-07-11 15:05:36 [+0800], quanyang.wang@...driver.com wrote:
> diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> index 116a91d90ac2..af34fb82f4bb 100644
> --- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> @@ -518,7 +518,7 @@ static int etm_enable_sysfs(struct coresight_device *csdev)
>  	struct etm_enable_arg arg = { };
>  	int ret;
>  
> -	spin_lock(&drvdata->spinlock);
> +	raw_spin_lock(&drvdata->spinlock);
>  
>  	/* sysfs needs to allocate and set a trace ID */
>  	ret = etm_read_alloc_trace_id(drvdata);

This is not going to work because etm_read_alloc_trace_id() acquires
later in the call chain id_map_lock which is a spinlock_t.
This should also lead to a splat like the one you complain about.

Sebastian