coresight: tmc: getting rid of multiple read access

Allowing multiple readers to access the trace data simultaniously
via sysFS provides no shortage of opportunity for race condition,
mandates two variable to be maintained (drvdata::read_count and
drvdata::reading), makes the code complex and provide little
advantages, if any.

This patch streamlines the read process by restricting trace data
access to a single user.  That way drvdata::read_count can
be eliminated and race conditions (along with faulty error handling)
in function tmc_open() and tmc_release() eliminated.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit f74debbea0885ebb65fb3fa4e598323f40b03f5f)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
index 6eb1665cfc9ce2ecff001ae49dde58f48f11fd48..60edf4d1968f2890af9bf86ca041cfbf83456c95 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
@@ -260,6 +260,11 @@ int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
 
        spin_lock_irqsave(&drvdata->spinlock, flags);
 
+       if (drvdata->reading) {
+               ret = -EBUSY;
+               goto out;
+       }
+
        /* There is no point in reading a TMC in HW FIFO mode */
        mode = readl_relaxed(drvdata->base + TMC_MODE);
        if (mode != TMC_MODE_CIRCULAR_BUFFER) {

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index ac37bf904fb7cd50e82b9425a7342c17bd5f5db6..d6999b457fb82868d6adfa83ed7d81bf5d2ae9cc 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -188,6 +188,10 @@ int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
                return -EINVAL;
 
        spin_lock_irqsave(&drvdata->spinlock, flags);
+       if (drvdata->reading) {
+               ret = -EBUSY;
+               goto out;
+       }
 
        /* If drvdata::buf is NULL the trace data has been read already */
        if (drvdata->buf == NULL) {

diff --git a/drivers/hwtracing/coresight/coresight-tmc.c b/drivers/hwtracing/coresight/coresight-tmc.c
index e8e12a9b917aff2c20b52f34c1891141ed8e4d6e..ae7525a2b94a6c2f48ee66f0fa26ed2c2f33ffa0 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-tmc.c
+++ b/drivers/hwtracing/coresight/coresight-tmc.c
@@ -95,7 +95,7 @@ static int tmc_read_prepare(struct tmc_drvdata *drvdata)
        return ret;
 }
 
-static void tmc_read_unprepare(struct tmc_drvdata *drvdata)
+static int tmc_read_unprepare(struct tmc_drvdata *drvdata)
 {
        int ret = 0;
 
@@ -113,21 +113,20 @@ static void tmc_read_unprepare(struct tmc_drvdata *drvdata)
 
        if (!ret)
                dev_info(drvdata->dev, "TMC read end\n");
+
+       return ret;
 }
 
 static int tmc_open(struct inode *inode, struct file *file)
 {
+       int ret;
        struct tmc_drvdata *drvdata = container_of(file->private_data,
                                                   struct tmc_drvdata, miscdev);
-       int ret = 0;
-
-       if (drvdata->read_count++)
-               goto out;
 
        ret = tmc_read_prepare(drvdata);
        if (ret)
                return ret;
-out:
+
        nonseekable_open(inode, file);
 
        dev_dbg(drvdata->dev, "%s: successfully opened\n", __func__);
@@ -167,19 +166,14 @@ static ssize_t tmc_read(struct file *file, char __user *data, size_t len,
 
 static int tmc_release(struct inode *inode, struct file *file)
 {
+       int ret;
        struct tmc_drvdata *drvdata = container_of(file->private_data,
                                                   struct tmc_drvdata, miscdev);
 
-       if (--drvdata->read_count) {
-               if (drvdata->read_count < 0) {
-                       dev_err(drvdata->dev, "mismatched close\n");
-                       drvdata->read_count = 0;
-               }
-               goto out;
-       }
+       ret = tmc_read_unprepare(drvdata);
+       if (ret)
+               return ret;
 
-       tmc_read_unprepare(drvdata);
-out:
        dev_dbg(drvdata->dev, "%s: released\n", __func__);
        return 0;
 }

diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
index df661903f83cf0e8a2d8d6be9c264ecc19785b4c..592eb149fe3a5b9dd687626450ff7e8afa877e82 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-tmc.h
+++ b/drivers/hwtracing/coresight/coresight-tmc.h
@@ -94,7 +94,6 @@ enum tmc_mem_intf_width {
  * @csdev:     component vitals needed by the framework.
  * @miscdev:   specifics to handle "/dev/xyz.tmc" entry.
  * @spinlock:  only one at a time pls.
- * @read_count:        manages preparation of buffer for reading.
  * @buf:       area of memory where trace data get sent.
  * @paddr:     DMA start location in RAM.
  * @vaddr:     virtual representation of @paddr.
@@ -109,7 +108,6 @@ struct tmc_drvdata {
        struct coresight_device *csdev;
        struct miscdevice       miscdev;
        spinlock_t              spinlock;
-       int                     read_count;
        bool                    reading;
        char                    *buf;
        dma_addr_t              paddr;