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Message-ID: <9c5a2f4a-7884-ac27-f9ee-ad8fe6f41ab1@arm.com>
Date:   Wed, 15 Nov 2023 16:39:21 +0000
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Subject: Re: [PATCH v3 1/4] coresight: ultrasoc-smb: Fix sleep while close
 preempt in enable_smb
Content-Language: en-US
To:     Junhao He <hejunhao3@huawei.com>, suzuki.poulose@arm.com
Cc:     coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linuxarm@huawei.com,
        jonathan.cameron@huawei.com, yangyicong@huawei.com,
        prime.zeng@hisilicon.com, u.kleine-koenig@pengutronix.de
References: <20231114133346.30489-1-hejunhao3@huawei.com>
 <20231114133346.30489-2-hejunhao3@huawei.com>
From:   James Clark <james.clark@arm.com>
In-Reply-To: <20231114133346.30489-2-hejunhao3@huawei.com>
Content-Type: text/plain; charset=UTF-8
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Precedence: bulk


On 14/11/2023 13:33, Junhao He wrote:
> When we to enable the SMB by perf, the perf sched will call perf_ctx_lock()
> to close system preempt in event_function_call(). But SMB::enable_smb() use
> mutex to lock the critical section, which may sleep.
> 
>  BUG: sleeping function called from invalid context at kernel/locking/mutex.c:580
>  in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 153023, name: perf
>  preempt_count: 2, expected: 0
>  RCU nest depth: 0, expected: 0
>  INFO: lockdep is turned off.
>  irq event stamp: 0
>  hardirqs last  enabled at (0): [<0000000000000000>] 0x0
>  hardirqs last disabled at (0): [<ffffa2983f5c5f40>] copy_process+0xae8/0x2b48
>  softirqs last  enabled at (0): [<ffffa2983f5c5f40>] copy_process+0xae8/0x2b48
>  softirqs last disabled at (0): [<0000000000000000>] 0x0
>  CPU: 2 PID: 153023 Comm: perf Kdump: loaded Tainted: G   W  O   6.5.0-rc4+ #1
> 
>  Call trace:
>  ...
>   __mutex_lock+0xbc/0xa70
>   mutex_lock_nested+0x34/0x48
>   smb_update_buffer+0x58/0x360 [ultrasoc_smb]
>   etm_event_stop+0x204/0x2d8 [coresight]
>   etm_event_del+0x1c/0x30 [coresight]
>   event_sched_out+0x17c/0x3b8
>   group_sched_out.part.0+0x5c/0x208
>   __perf_event_disable+0x15c/0x210
>   event_function+0xe0/0x230
>   remote_function+0xb4/0xe8
>   generic_exec_single+0x160/0x268
>   smp_call_function_single+0x20c/0x2a0
>   event_function_call+0x20c/0x220
>   _perf_event_disable+0x5c/0x90
>   perf_event_for_each_child+0x58/0xc0
>   _perf_ioctl+0x34c/0x1250
>   perf_ioctl+0x64/0x98
>  ...
> 
> Use spinlock to replace mutex to control driver data access to one at a
> time. The function copy_to_user() may sleep, it cannot be in a spinlock
> context, so we can't simply replace it in smb_read(). But we can ensure
> that only one user gets the SMB device fd by smb_open(), so remove the
> locks from smb_read() and buffer synchronization is guaranteed by the user.
> 
> Fixes: 06f5c2926aaa ("drivers/coresight: Add UltraSoc System Memory Buffer driver")
> Signed-off-by: Junhao He <hejunhao3@huawei.com>

Reviewed-by: James Clark <james.clark@arm.com>

> ---
>  drivers/hwtracing/coresight/ultrasoc-smb.c | 35 +++++++++-------------
>  drivers/hwtracing/coresight/ultrasoc-smb.h |  6 ++--
>  2 files changed, 17 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.c b/drivers/hwtracing/coresight/ultrasoc-smb.c
> index e9a32a97fbee..0a0fe9fcc57f 100644
> --- a/drivers/hwtracing/coresight/ultrasoc-smb.c
> +++ b/drivers/hwtracing/coresight/ultrasoc-smb.c
> @@ -99,7 +99,7 @@ static int smb_open(struct inode *inode, struct file *file)
>  					struct smb_drv_data, miscdev);
>  	int ret = 0;
>  
> -	mutex_lock(&drvdata->mutex);
> +	spin_lock(&drvdata->spinlock);
>  
>  	if (drvdata->reading) {
>  		ret = -EBUSY;
> @@ -115,7 +115,7 @@ static int smb_open(struct inode *inode, struct file *file)
>  
>  	drvdata->reading = true;
>  out:
> -	mutex_unlock(&drvdata->mutex);
> +	spin_unlock(&drvdata->spinlock);
>  
>  	return ret;
>  }
> @@ -132,10 +132,8 @@ static ssize_t smb_read(struct file *file, char __user *data, size_t len,
>  	if (!len)
>  		return 0;
>  
> -	mutex_lock(&drvdata->mutex);
> -
>  	if (!sdb->data_size)
> -		goto out;
> +		return 0;
>  
>  	to_copy = min(sdb->data_size, len);
>  
> @@ -145,20 +143,15 @@ static ssize_t smb_read(struct file *file, char __user *data, size_t len,
>  
>  	if (copy_to_user(data, sdb->buf_base + sdb->buf_rdptr, to_copy)) {
>  		dev_dbg(dev, "Failed to copy data to user\n");
> -		to_copy = -EFAULT;
> -		goto out;
> +		return -EFAULT;
>  	}
>  
>  	*ppos += to_copy;
> -
>  	smb_update_read_ptr(drvdata, to_copy);
> -
> -	dev_dbg(dev, "%zu bytes copied\n", to_copy);
> -out:
>  	if (!sdb->data_size)
>  		smb_reset_buffer(drvdata);
> -	mutex_unlock(&drvdata->mutex);
>  
> +	dev_dbg(dev, "%zu bytes copied\n", to_copy);
>  	return to_copy;
>  }
>  
> @@ -167,9 +160,9 @@ static int smb_release(struct inode *inode, struct file *file)
>  	struct smb_drv_data *drvdata = container_of(file->private_data,
>  					struct smb_drv_data, miscdev);
>  
> -	mutex_lock(&drvdata->mutex);
> +	spin_lock(&drvdata->spinlock);
>  	drvdata->reading = false;
> -	mutex_unlock(&drvdata->mutex);
> +	spin_unlock(&drvdata->spinlock);
>  
>  	return 0;
>  }
> @@ -262,7 +255,7 @@ static int smb_enable(struct coresight_device *csdev, enum cs_mode mode,
>  	struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
>  	int ret = 0;
>  
> -	mutex_lock(&drvdata->mutex);
> +	spin_lock(&drvdata->spinlock);
>  
>  	/* Do nothing, the trace data is reading by other interface now */
>  	if (drvdata->reading) {
> @@ -294,7 +287,7 @@ static int smb_enable(struct coresight_device *csdev, enum cs_mode mode,
>  
>  	dev_dbg(&csdev->dev, "Ultrasoc SMB enabled\n");
>  out:
> -	mutex_unlock(&drvdata->mutex);
> +	spin_unlock(&drvdata->spinlock);
>  
>  	return ret;
>  }
> @@ -304,7 +297,7 @@ static int smb_disable(struct coresight_device *csdev)
>  	struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
>  	int ret = 0;
>  
> -	mutex_lock(&drvdata->mutex);
> +	spin_lock(&drvdata->spinlock);
>  
>  	if (drvdata->reading) {
>  		ret = -EBUSY;
> @@ -327,7 +320,7 @@ static int smb_disable(struct coresight_device *csdev)
>  
>  	dev_dbg(&csdev->dev, "Ultrasoc SMB disabled\n");
>  out:
> -	mutex_unlock(&drvdata->mutex);
> +	spin_unlock(&drvdata->spinlock);
>  
>  	return ret;
>  }
> @@ -408,7 +401,7 @@ static unsigned long smb_update_buffer(struct coresight_device *csdev,
>  	if (!buf)
>  		return 0;
>  
> -	mutex_lock(&drvdata->mutex);
> +	spin_lock(&drvdata->spinlock);
>  
>  	/* Don't do anything if another tracer is using this sink. */
>  	if (atomic_read(&csdev->refcnt) != 1)
> @@ -432,7 +425,7 @@ static unsigned long smb_update_buffer(struct coresight_device *csdev,
>  	if (!buf->snapshot && lost)
>  		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
>  out:
> -	mutex_unlock(&drvdata->mutex);
> +	spin_unlock(&drvdata->spinlock);
>  
>  	return data_size;
>  }
> @@ -590,7 +583,7 @@ static int smb_probe(struct platform_device *pdev)
>  		return ret;
>  	}
>  
> -	mutex_init(&drvdata->mutex);
> +	spin_lock_init(&drvdata->spinlock);
>  	drvdata->pid = -1;
>  
>  	ret = smb_register_sink(pdev, drvdata);
> diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.h b/drivers/hwtracing/coresight/ultrasoc-smb.h
> index d2e14e8d2c8a..82a44c14a882 100644
> --- a/drivers/hwtracing/coresight/ultrasoc-smb.h
> +++ b/drivers/hwtracing/coresight/ultrasoc-smb.h
> @@ -8,7 +8,7 @@
>  #define _ULTRASOC_SMB_H
>  
>  #include <linux/miscdevice.h>
> -#include <linux/mutex.h>
> +#include <linux/spinlock.h>
>  
>  /* Offset of SMB global registers */
>  #define SMB_GLB_CFG_REG		0x00
> @@ -105,7 +105,7 @@ struct smb_data_buffer {
>   * @csdev:	Component vitals needed by the framework.
>   * @sdb:	Data buffer for SMB.
>   * @miscdev:	Specifics to handle "/dev/xyz.smb" entry.
> - * @mutex:	Control data access to one at a time.
> + * @spinlock:	Control data access to one at a time.
>   * @reading:	Synchronise user space access to SMB buffer.
>   * @pid:	Process ID of the process being monitored by the
>   *		session that is using this component.
> @@ -116,7 +116,7 @@ struct smb_drv_data {
>  	struct coresight_device	*csdev;
>  	struct smb_data_buffer sdb;
>  	struct miscdevice miscdev;
> -	struct mutex mutex;
> +	spinlock_t spinlock;
>  	bool reading;
>  	pid_t pid;
>  	enum cs_mode mode;