greybus: loopback: make loopback code thread safe

Current code allows a sysfs callback and a kernel worker thread to write
all over and act upon data that could be in the process of being updated by
the other. This patch adds a reasonably coarse mutex to enscure sync
between the two.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

diff --git a/drivers/staging/greybus/loopback.c b/drivers/staging/greybus/loopback.c
index 5f7c1a6256ccaaa1c8c19b32150d8063d4a14380..afba4225defdd4c7ded42230afeacaeacee60d78 100644 (file)
--- a/drivers/staging/greybus/loopback.c
+++ b/drivers/staging/greybus/loopback.c
@@ -8,6 +8,7 @@
  */
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/kthread.h>
 #include <linux/delay.h>
@@ -30,6 +31,7 @@ struct gb_loopback {
        u8 version_major;
        u8 version_minor;
 
+       struct mutex mutex;
        struct task_struct *task;
        wait_queue_head_t wq;
 
@@ -101,10 +103,13 @@ static ssize_t field##_store(struct device *dev,                  \
        struct gb_connection *connection = to_gb_connection(dev);       \
        struct gb_loopback *gb =                                        \
                (struct gb_loopback *)connection->private;              \
+       mutex_lock(&gb->mutex);                                         \
        ret = sscanf(buf, "%"#type, &gb->field);                        \
        if (ret != 1)                                                   \
-               return -EINVAL;                                         \
-       gb_loopback_check_attr(gb);                                     \
+               len = -EINVAL;                                          \
+       else                                                            \
+               gb_loopback_check_attr(gb);                             \
+       mutex_unlock(&gb->mutex);                                       \
        return len;                                                     \
 }                                                                      \
 static DEVICE_ATTR_RW(field)
@@ -385,6 +390,7 @@ static void gb_loopback_calculate_stats(struct gb_loopback *gb)
 static int gb_loopback_fn(void *data)
 {
        int error = 0;
+       int ms_wait;
        struct gb_loopback *gb = (struct gb_loopback *)data;
 
        while (1) {
@@ -393,6 +399,8 @@ static int gb_loopback_fn(void *data)
                                                 kthread_should_stop());
                if (kthread_should_stop())
                        break;
+
+               mutex_lock(&gb->mutex);
                if (gb->iteration_max) {
                        if (gb->iteration_count < gb->iteration_max) {
                                gb->iteration_count++;
@@ -400,6 +408,7 @@ static int gb_loopback_fn(void *data)
                                             "iteration_count");
                        } else {
                                gb->type = 0;
+                               mutex_unlock(&gb->mutex);
                                continue;
                        }
                }
@@ -412,8 +421,10 @@ static int gb_loopback_fn(void *data)
                if (error)
                        gb->error++;
                gb_loopback_calculate_stats(gb);
-               if (gb->ms_wait)
-                       msleep(gb->ms_wait);
+               ms_wait = gb->ms_wait;
+               mutex_unlock(&gb->mutex);
+               if (ms_wait)
+                       msleep(ms_wait);
        }
        return 0;
 }
@@ -448,6 +459,7 @@ static int gb_loopback_connection_init(struct gb_connection *connection)
 
        gb_loopback_reset_stats(gb);
        init_waitqueue_head(&gb->wq);
+       mutex_init(&gb->mutex);
        gb->task = kthread_run(gb_loopback_fn, gb, "gb_loopback");
        if (IS_ERR(gb->task)) {
                retval = PTR_ERR(gb->task);