fs/inode: using rwsem lock as inode_lock to avoid deadlock

Example:
When executing "df -h" on Core A to view mount information, this
process will traverse inode nodes, thereby holding the inode_lock.
Since the inode type of the mount point may be rpmsgfs, it will fetch statfs
information from another Core B.

Meanwhile, rcS on Core B needs to obtain file information from Core A,
which will be achieved by fetching stat information through rpmsgfs.
When this message arrives at Core A, a deadlock can occur between Core A's
rptun ap and nsh task.

However, both of these places involve read operations only, thus a reader-writer lock
can be utilized to prevent such a deadlock.

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>

fs/driver/fs_registerblockdriver.c

@@ -74,12 +74,7 @@ int register_blockdriver(FAR const char *path,
    * valid data.
    */
 
-  ret = inode_lock();
-  if (ret < 0)
-    {
-      return ret;
-    }
-
+  inode_lock();
   ret = inode_reserve(path, mode, &node);
   if (ret >= 0)
     {

fs/driver/fs_registerdriver.c

@@ -73,12 +73,7 @@ int register_driver(FAR const char *path,
    * will have a momentarily bad structure.
    */
 
-  ret = inode_lock();
-  if (ret < 0)
-    {
-      return ret;
-    }
-
+  inode_lock();
   ret = inode_reserve(path, mode, &node);
   if (ret >= 0)
     {

fs/driver/fs_registermtddriver.c

@@ -74,12 +74,7 @@ int register_mtddriver(FAR const char *path, FAR struct mtd_dev_s *mtd,
    * valid data.
    */
 
-  ret = inode_lock();
-  if (ret < 0)
-    {
-      return ret;
-    }
-
+  inode_lock();
   ret = inode_reserve(path, mode, &node);
   if (ret >= 0)
     {

fs/driver/fs_registerpipedriver.c

@@ -72,12 +72,7 @@ int register_pipedriver(FAR const char *path,
    * will have a momentarily bad structure.
    */
 
-  ret = inode_lock();
-  if (ret < 0)
-    {
-      return ret;
-    }
-
+  inode_lock();
   ret = inode_reserve(path, mode, &node);
   if (ret >= 0)
     {

fs/driver/fs_unregisterblockdriver.c

@@ -45,17 +45,11 @@ int unregister_blockdriver(FAR const char *path)
 {
   int ret;
 
-  ret = inode_lock();
-  if (ret >= 0)
-    {
-      ret = inode_remove(path);
-      inode_unlock();
+  inode_lock();
+  ret = inode_remove(path);
+  inode_unlock();
 #ifdef CONFIG_FS_NOTIFY
-      notify_unlink(path);
+  notify_unlink(path);
 #endif
-      return OK;
-    }
-
-  inode_unlock();
   return ret;
 }

fs/driver/fs_unregisterdriver.c

@@ -55,17 +55,11 @@ int unregister_driver(FAR const char *path)
 
   /* If unlink failed, only remove inode. */
 
-  ret = inode_lock();
-  if (ret >= 0)
-    {
-      ret = inode_remove(path);
-      inode_unlock();
+  inode_lock();
+  ret = inode_remove(path);
+  inode_unlock();
 #ifdef CONFIG_FS_NOTIFY
-      notify_unlink(path);
+  notify_unlink(path);
 #endif
-      return OK;
-    }
-
-  inode_unlock();
   return ret;
 }

fs/driver/fs_unregistermtddriver.c

@@ -46,17 +46,11 @@ int unregister_mtddriver(FAR const char *path)
 {
   int ret;
 
-  ret = inode_lock();
-  if (ret >= 0)
-    {
-      ret = inode_remove(path);
-      inode_unlock();
+  inode_lock();
+  ret = inode_remove(path);
+  inode_unlock();
 #ifdef CONFIG_FS_NOTIFY
-      notify_unlink(path);
+  notify_unlink(path);
 #endif
-      return OK;
-    }
-
-  inode_unlock();
   return ret;
 }

fs/driver/fs_unregisterpipedriver.c

@@ -47,18 +47,12 @@ int unregister_pipedriver(FAR const char *path)
 {
   int ret;
 
-  ret = inode_lock();
-  if (ret >= 0)
-    {
-      ret = inode_remove(path);
-      inode_unlock();
+  inode_lock();
+  ret = inode_remove(path);
+  inode_unlock();
 #ifdef CONFIG_FS_NOTIFY
-      notify_unlink(path);
+  notify_unlink(path);
 #endif
-      return OK;
-    }
-
-  inode_unlock();
   return ret;
 }
 

fs/inode/fs_foreachinode.c

@@ -184,12 +184,9 @@ int foreach_inode(foreach_inode_t handler, FAR void *arg)
 
   /* Start the recursion at the root inode */
 
-  ret = inode_lock();
-  if (ret >= 0)
-    {
-      ret = foreach_inodelevel(g_root_inode->i_child, info);
-      inode_unlock();
-    }
+  inode_rlock();
+  ret = foreach_inodelevel(g_root_inode->i_child, info);
+  inode_runlock();
 
   /* Free the info structure and return the result */
 
@@ -208,12 +205,9 @@ int foreach_inode(foreach_inode_t handler, FAR void *arg)
 
   /* Start the recursion at the root inode */
 
-  ret = inode_lock();
-  if (ret >= 0)
-    {
-      ret = foreach_inodelevel(g_root_inode->i_child, &info);
-      inode_unlock();
-    }
+  inode_rlock();
+  ret = foreach_inodelevel(g_root_inode->i_child, &info);
+  inode_runlock();
 
   return ret;
 

fs/inode/fs_inode.c

@@ -22,14 +22,8 @@
  * Included Files
  ****************************************************************************/
 
-#include <nuttx/config.h>
-
-#include <unistd.h>
-#include <assert.h>
-#include <errno.h>
-
 #include <nuttx/fs/fs.h>
-#include <nuttx/mutex.h>
+#include <nuttx/rwsem.h>
 
 #include "inode/inode.h"
 
@@ -45,7 +39,7 @@
  * Private Data
  ****************************************************************************/
 
-static rmutex_t g_inode_lock = NXRMUTEX_INITIALIZER;
+static rw_semaphore_t g_inode_lock = RWSEM_INITIALIZER;
 
 /****************************************************************************
  * Public Functions
@@ -71,24 +65,50 @@ void inode_initialize(void)
  * Name: inode_lock
  *
  * Description:
- *   Get exclusive access to the in-memory inode tree (g_inode_sem).
+ *   Get writeable exclusive access to the in-memory inode tree.
+ *
+ ****************************************************************************/
+
+void inode_lock(void)
+{
+  down_write(&g_inode_lock);
+}
+
+/****************************************************************************
+ * Name: inode_rlock
+ *
+ * Description:
+ *   Get readable exclusive access to the in-memory inode tree.
  *
  ****************************************************************************/
 
-int inode_lock(void)
+void inode_rlock(void)
 {
-  return nxrmutex_lock(&g_inode_lock);
+  down_read(&g_inode_lock);
 }
 
 /****************************************************************************
  * Name: inode_unlock
  *
  * Description:
- *   Relinquish exclusive access to the in-memory inode tree (g_inode_sem).
+ *   Relinquish writeable exclusive access to the in-memory inode tree.
  *
  ****************************************************************************/
 
 void inode_unlock(void)
 {
-  DEBUGVERIFY(nxrmutex_unlock(&g_inode_lock));
+  up_write(&g_inode_lock);
+}
+
+/****************************************************************************
+ * Name: inode_runlock
+ *
+ * Description:
+ *   Relinquish read exclusive access to the in-memory inode tree.
+ *
+ ****************************************************************************/
+
+void inode_runlock(void)
+{
+  up_read(&g_inode_lock);
 }

fs/inode/fs_inodeaddref.c

@@ -43,12 +43,10 @@
 
 int inode_addref(FAR struct inode *inode)
 {
-  int ret = OK;
-
   if (inode)
     {
       atomic_fetch_add(&inode->i_crefs, 1);
     }
 
-  return ret;
+  return OK;
 }

fs/inode/fs_inodefind.c

@@ -55,12 +55,7 @@ int inode_find(FAR struct inode_search_s *desc)
    * references on the node.
    */
 
-  ret = inode_lock();
-  if (ret < 0)
-    {
-      return ret;
-    }
-
+  inode_lock();
   ret = inode_search(desc);
   if (ret >= 0)
     {

fs/inode/inode.h

@@ -170,22 +170,42 @@ void inode_initialize(void);
  * Name: inode_lock
  *
  * Description:
- *   Get exclusive access to the in-memory inode tree (tree_sem).
+ *   Get writeable exclusive access to the in-memory inode tree.
  *
  ****************************************************************************/
 
-int inode_lock(void);
+void inode_lock(void);
+
+/****************************************************************************
+ * Name: inode_rlock
+ *
+ * Description:
+ *   Get readable exclusive access to the in-memory inode tree.
+ *
+ ****************************************************************************/
+
+void inode_rlock(void);
 
 /****************************************************************************
  * Name: inode_unlock
  *
  * Description:
- *   Relinquish exclusive access to the in-memory inode tree (tree_sem).
+ *   Relinquish writeable exclusive access to the in-memory inode tree.
  *
  ****************************************************************************/
 
 void inode_unlock(void);
 
+/****************************************************************************
+ * Name: inode_runlock
+ *
+ * Description:
+ *   Relinquish read exclusive access to the in-memory inode tree.
+ *
+ ****************************************************************************/
+
+void inode_runlock(void);
+
 /****************************************************************************
  * Name: inode_search
  *

fs/mount/fs_automount.c

@@ -401,11 +401,7 @@ static int automount_findinode(FAR const char *path)
 
   /* Get exclusive access to the in-memory inode tree. */
 
-  ret = inode_lock();
-  if (ret < 0)
-    {
-      return ret;
-    }
+  inode_rlock();
 
   /* Find the inode */
 
@@ -439,7 +435,7 @@ static int automount_findinode(FAR const char *path)
 
   /* Relinquish our exclusive access to the inode try and return the result */
 
-  inode_unlock();
+  inode_runlock();
   RELEASE_SEARCH(&desc);
   return ret;
 }

fs/mount/fs_mount.c

@@ -367,12 +367,7 @@ int nx_mount(FAR const char *source, FAR const char *target,
       goto errout;
     }
 
-  ret = inode_lock();
-  if (ret < 0)
-    {
-      goto errout_with_inode;
-    }
-
+  inode_lock();
 #ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
   /* Check if the inode already exists */
 
@@ -462,7 +457,7 @@ int nx_mount(FAR const char *source, FAR const char *target,
 #else
   ret = mops->bind(NULL, data, &fshandle);
 #endif
-  DEBUGVERIFY(inode_lock() >= 0);
+  inode_lock();
   if (ret < 0)
     {
       /* The inode is unhappy with the driver for some reason.  Back out

fs/mount/fs_umount2.c

@@ -110,12 +110,7 @@ int nx_umount2(FAR const char *target, unsigned int flags)
 
   /* Hold the semaphore through the unbind logic */
 
-  ret = inode_lock();
-  if (ret < 0)
-    {
-      goto errout_with_mountpt;
-    }
-
+  inode_lock();
   ret = mountpt_inode->u.i_mops->unbind(mountpt_inode->i_private,
                                        &blkdrvr_inode, flags);
   if (ret < 0)