From a497aebcfa95aa20044e5ab3b57614c0f4383b6b Mon Sep 17 00:00:00 2001
From: Xiang Xiao <xiaoxiang@xiaomi.com>
Date: Sun, 27 Jan 2019 10:08:07 -0600
Subject: [PATCH] drivers/timers/rtc.c:  Protect the RTC state with a
 semaphore.

---
 drivers/timers/rtc.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/timers/rtc.c b/drivers/timers/rtc.c
index 93f702deee..e6338aae4e 100644
--- a/drivers/timers/rtc.c
+++ b/drivers/timers/rtc.c
@@ -40,6 +40,7 @@
 #include <nuttx/config.h>
 
 #include <sys/types.h>
+#include <semaphore.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <string.h>
@@ -67,6 +68,7 @@ struct rtc_alarminfo_s
 struct rtc_upperhalf_s
 {
   FAR struct rtc_lowerhalf_s *lower;  /* Contained lower half driver */
+  sem_t exclsem;                      /* Supports mutual exclusion */
 
 #ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
   uint8_t crefs;                      /* Number of open references */
@@ -171,6 +173,7 @@ static void rtc_destroy(FAR struct rtc_upperhalf_s *upper)
 
   /* And free our container */
 
+  nxsem_destroy(&upper->exclsem);
   kmm_free(upper);
 }
 #endif
@@ -248,6 +251,7 @@ static int rtc_open(FAR struct file *filep)
 {
   FAR struct inode *inode;
   FAR struct rtc_upperhalf_s *upper;
+  int ret;
 
   /* Get the reference to our internal state structure from the inode
    * structure.
@@ -258,10 +262,19 @@ static int rtc_open(FAR struct file *filep)
   DEBUGASSERT(inode && inode->i_private);
   upper = inode->i_private;
 
+  /* Get exclusive access to the device structures */
+
+  ret = nxsem_wait(&upper->exclsem);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
   /* Increment the count of open references on the RTC driver */
 
   upper->crefs++;
   DEBUGASSERT(upper->crefs > 0);
+  nxsem_post(&upper->exclsem);
   return OK;
 }
 #endif
@@ -275,6 +288,7 @@ static int rtc_close(FAR struct file *filep)
 {
   FAR struct inode *inode;
   FAR struct rtc_upperhalf_s *upper;
+  int ret;
 
   /* Get the reference to our internal state structure from the inode
    * structure.
@@ -285,10 +299,19 @@ static int rtc_close(FAR struct file *filep)
   DEBUGASSERT(inode && inode->i_private);
   upper = inode->i_private;
 
+  /* Get exclusive access to the device structures */
+
+  ret = nxsem_wait(&upper->exclsem);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
   /* Decrement the count of open references on the RTC driver */
 
   DEBUGASSERT(upper->crefs > 0);
   upper->crefs--;
+  nxsem_post(&upper->exclsem);
 
   /* If the count has decremented to zero and the driver has been unlinked,
    * then commit Hara-Kiri now.
@@ -343,6 +366,14 @@ static int rtc_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
   upper = inode->i_private;
   DEBUGASSERT(upper->lower && upper->lower->ops);
 
+  /* Get exclusive access to the device structures */
+
+  ret = nxsem_wait(&upper->exclsem);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
   /* We simply forward all ioctl() commands to the lower half.  The upper
    * half is nothing more than a thin driver shell over the lower level
    * RTC implementation.
@@ -726,6 +757,7 @@ static int rtc_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
       break;
     }
 
+  nxsem_post(&upper->exclsem);
   return ret;
 }
 
@@ -737,6 +769,7 @@ static int rtc_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
 static int rtc_unlink(FAR struct inode *inode)
 {
   FAR struct rtc_upperhalf_s *upper;
+  int ret;
 
   /* Get the reference to our internal state structure from the inode
    * structure.
@@ -745,9 +778,18 @@ static int rtc_unlink(FAR struct inode *inode)
   DEBUGASSERT(inode && inode->i_private);
   upper = inode->i_private;
 
+  /* Get exclusive access to the device structures */
+
+  ret = nxsem_wait(&upper->exclsem);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
   /* Indicate that the driver has been unlinked */
 
   upper->unlinked = true;
+  nxsem_post(&upper->exclsem);
 
   /* If there are no further open references to the driver, then commit
    * Hara-Kiri now.
@@ -804,6 +846,7 @@ int rtc_initialize(int minor, FAR struct rtc_lowerhalf_s *lower)
   /* Initialize the upper half container */
 
   upper->lower = lower;     /* Contain lower half driver */
+  nxsem_init(&upper->exclsem, 0, 1);
 
 #ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
   upper->crefs = 0;         /* No open references */
@@ -821,6 +864,7 @@ int rtc_initialize(int minor, FAR struct rtc_lowerhalf_s *lower)
   ret = register_driver(devpath, &rtc_fops, 0666, upper);
   if (ret < 0)
     {
+      nxsem_destroy(&upper->exclsem);
       kmm_free(upper);
       return ret;
     }