Re: [RFC PATCH 1/5] fsi/scom: Add mutex around FSI2PIB accesses

[Eddie James]

On 06/12/2018 12:19 AM, Benjamin Herrenschmidt wrote:

Otherwise, multiple clients can open the driver and attempt
to access the PIB at the same time, thus clobbering each other
in the process.

Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>

Reviewed-by: Eddie James <eaja...@linux.vnet.ibm.com>

---
  drivers/fsi/fsi-scom.c | 25 ++++++++++++++++++-------
  1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/drivers/fsi/fsi-scom.c b/drivers/fsi/fsi-scom.c
index c8eb5e5b94a7..3cba0eb645e1 100644
--- a/drivers/fsi/fsi-scom.c
+++ b/drivers/fsi/fsi-scom.c
@@ -37,6 +37,7 @@ struct scom_device {
        struct list_head link;
        struct fsi_device *fsi_dev;
        struct miscdevice mdev;
+       struct mutex lock;
        char    name[32];
        int idx;
  };
@@ -53,21 +54,26 @@ static int put_scom(struct scom_device *scom_dev, uint64_t 
value,
        int rc;
        uint32_t data;

+       mutex_lock(&scom_dev->lock);
+
        data = cpu_to_be32((value >> 32) & 0xffffffff);
        rc = fsi_device_write(scom_dev->fsi_dev, SCOM_DATA0_REG, &data,
                                sizeof(uint32_t));
        if (rc)
-               return rc;
+               goto bail;

        data = cpu_to_be32(value & 0xffffffff);
        rc = fsi_device_write(scom_dev->fsi_dev, SCOM_DATA1_REG, &data,
                                sizeof(uint32_t));
        if (rc)
-               return rc;
+               goto bail;

        data = cpu_to_be32(SCOM_WRITE_CMD | addr);
-       return fsi_device_write(scom_dev->fsi_dev, SCOM_CMD_REG, &data,
+       rc = fsi_device_write(scom_dev->fsi_dev, SCOM_CMD_REG, &data,
                                sizeof(uint32_t));
+ bail:
+       mutex_unlock(&scom_dev->lock);
+       return rc;
  }

  static int get_scom(struct scom_device *scom_dev, uint64_t *value,
@@ -76,27 +82,31 @@ static int get_scom(struct scom_device *scom_dev, uint64_t 
*value,
        uint32_t result, data;
        int rc;

+
+       mutex_lock(&scom_dev->lock);
        *value = 0ULL;
        data = cpu_to_be32(addr);
        rc = fsi_device_write(scom_dev->fsi_dev, SCOM_CMD_REG, &data,
                                sizeof(uint32_t));
        if (rc)
-               return rc;
+               goto bail;

        rc = fsi_device_read(scom_dev->fsi_dev, SCOM_DATA0_REG, &result,
                                sizeof(uint32_t));
        if (rc)
-               return rc;
+               goto bail;

        *value |= (uint64_t)cpu_to_be32(result) << 32;
        rc = fsi_device_read(scom_dev->fsi_dev, SCOM_DATA1_REG, &result,
                                sizeof(uint32_t));
        if (rc)
-               return rc;
+               goto bail;

        *value |= cpu_to_be32(result);

-       return 0;
+ bail:
+       mutex_unlock(&scom_dev->lock);
+       return rc;
  }

  static ssize_t scom_read(struct file *filep, char __user *buf, size_t len,
@@ -183,6 +193,7 @@ static int scom_probe(struct device *dev)
        if (!scom)
                return -ENOMEM;

+       mutex_init(&scom->lock);
        scom->idx = ida_simple_get(&scom_ida, 1, INT_MAX, GFP_KERNEL);
        snprintf(scom->name, sizeof(scom->name), "scom%d", scom->idx);
        scom->fsi_dev = fsi_dev;