diff --git a/include/nuttx/fs/fs.h b/include/nuttx/fs/fs.h
index 121bf0bc158..be7c122be28 100644
--- a/include/nuttx/fs/fs.h
+++ b/include/nuttx/fs/fs.h
@@ -1230,19 +1230,6 @@ int find_mtddriver(FAR const char *pathname, FAR struct inode **ppinode);
 
 int close_mtddriver(FAR struct inode *pinode);
 
-/****************************************************************************
- * Name: lib_flushall
- *
- * Description:
- *   Called either (1) by the OS when a task exits, or (2) from fflush()
- *   when a NULL stream argument is provided.
- *
- ****************************************************************************/
-
-#ifdef CONFIG_FILE_STREAM
-int lib_flushall(FAR struct streamlist *list);
-#endif
-
 /****************************************************************************
  * Name: file_read
  *
diff --git a/include/stdio.h b/include/stdio.h
index cc7f10441c8..1af9e229357 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -99,7 +99,6 @@
 
 #define setlinebuf(stream)   setvbuf(stream, NULL, _IOLBF, 0)
 
-#define clearerr_unlocked(stream) clearerr(stream)
 #define feof_unlocked(stream)     feof(stream)
 #define ferror_unlocked(stream)   ferror(stream)
 #define fileno_unlocked(stream)   fileno(stream)
@@ -140,8 +139,10 @@ extern "C"
 /* Operations on streams (FILE) */
 
 void   clearerr(FAR FILE *stream);
+void   clearerr_unlocked(FAR FILE *stream);
 int    fclose(FAR FILE *stream);
 int    fflush(FAR FILE *stream);
+int    fflush_unlocked(FAR FILE *stream);
 int    feof(FAR FILE *stream);
 int    ferror(FAR FILE *stream);
 int    fileno(FAR FILE *stream);
@@ -174,6 +175,7 @@ size_t fwrite(FAR const void *ptr, size_t size, size_t n_items,
 size_t fwrite_unlocked(FAR const void *ptr, size_t size, size_t n_items,
                        FAR FILE *stream);
 int     getc(FAR FILE *stream);
+int     getc_unlocked(FAR FILE *stream);
 int     getchar(void);
 int     getchar_unlocked(void);
 ssize_t getdelim(FAR char **lineptr, size_t *n, int delimiter,
diff --git a/include/wchar.h b/include/wchar.h
index d37fb235543..45db6605419 100644
--- a/include/wchar.h
+++ b/include/wchar.h
@@ -162,6 +162,7 @@ size_t            mbsrtowcs(FAR wchar_t *, FAR const char **, size_t,
 wint_t            putwc(wchar_t, FILE *);
 wint_t            putwc_unlocked(wchar_t, FAR FILE *);
 wint_t            putwchar(wchar_t);
+wint_t            putwchar_unlocked(wchar_t);
 int               swprintf(FAR wchar_t *, size_t, FAR const wchar_t *, ...);
 int               swscanf(FAR const wchar_t *, FAR const wchar_t *, ...);
 wint_t            ungetwc(wint_t, FILE *);
diff --git a/libs/libc/libc.h b/libs/libc/libc.h
index ba339d48d56..8e3a038fb5a 100644
--- a/libs/libc/libc.h
+++ b/libs/libc/libc.h
@@ -209,6 +209,13 @@ FAR char *lib_fgets(FAR char *buf, size_t buflen, FILE *stream,
 FAR char *lib_fgets_unlocked(FAR char *buf, size_t buflen, FILE *stream,
                              bool keepnl, bool consume);
 
+/* Defined in lib_flushall.c */
+
+#ifdef CONFIG_FILE_STREAM
+int lib_flushall(FAR struct streamlist *list);
+int lib_flushall_unlocked(FAR struct streamlist *list);
+#endif
+
 /* Defined in lib_libfflush.c */
 
 ssize_t lib_fflush(FAR FILE *stream);
diff --git a/libs/libc/stdio/lib_clearerr.c b/libs/libc/stdio/lib_clearerr.c
index 39e6b74da90..faee4a973e7 100644
--- a/libs/libc/stdio/lib_clearerr.c
+++ b/libs/libc/stdio/lib_clearerr.c
@@ -46,8 +46,15 @@
  *
  ****************************************************************************/
 
-void clearerr(FAR FILE *stream)
+void clearerr_unlocked(FAR FILE *stream)
 {
   stream->fs_flags &= (__FS_FLAG_LBF | __FS_FLAG_UBF);
 }
+
+void clearerr(FAR FILE *stream)
+{
+  flockfile(stream);
+  clearerr_unlocked(stream);
+  funlockfile(stream);
+}
 #endif /* CONFIG_FILE_STREAM */
diff --git a/libs/libc/stdio/lib_fflush.c b/libs/libc/stdio/lib_fflush.c
index cbe4e7a6026..5c461f4e3d3 100644
--- a/libs/libc/stdio/lib_fflush.c
+++ b/libs/libc/stdio/lib_fflush.c
@@ -52,13 +52,48 @@
  *
  ****************************************************************************/
 
+int fflush_unlocked(FAR FILE *stream)
+{
+  int ret;
+
+  /* Is the stream argument NULL? */
+
+  if (stream == NULL)
+    {
+      /* Yes... then this is a request to flush all streams */
+
+      ret = lib_flushall_unlocked(lib_get_streams());
+    }
+  else
+    {
+      ret = lib_fflush_unlocked(stream);
+    }
+
+  /* Check the return value */
+
+  if (ret < 0)
+    {
+      /* An error occurred during the flush AND/OR we were unable to flush
+       * all of the buffered write data. Set the errno value.
+       */
+
+      set_errno(-ret);
+
+      /* And return EOF on failure. */
+
+      return EOF;
+    }
+
+  return OK;
+}
+
 int fflush(FAR FILE *stream)
 {
   int ret;
 
   /* Is the stream argument NULL? */
 
-  if (!stream)
+  if (stream == NULL)
     {
       /* Yes... then this is a request to flush all streams */
 
diff --git a/libs/libc/stdio/lib_fputwc.c b/libs/libc/stdio/lib_fputwc.c
index 95248598fde..5aab48bfe63 100644
--- a/libs/libc/stdio/lib_fputwc.c
+++ b/libs/libc/stdio/lib_fputwc.c
@@ -64,7 +64,7 @@ wint_t fputwc_unlocked(wchar_t c, FAR FILE *f)
 
   if (isascii(c))
     {
-      c = putc(c, f);
+      c = putc_unlocked(c, f);
     }
   else
     {
diff --git a/libs/libc/stdio/lib_libflushall.c b/libs/libc/stdio/lib_libflushall.c
index 225482cb3ce..2c4f37c592c 100644
--- a/libs/libc/stdio/lib_libflushall.c
+++ b/libs/libc/stdio/lib_libflushall.c
@@ -45,6 +45,54 @@
  *
  ****************************************************************************/
 
+int lib_flushall_unlocked(FAR struct streamlist *list)
+{
+  int lasterrno = OK;
+  int ret;
+
+  /* Make sure that there are streams associated with this thread */
+
+  if (list != NULL)
+    {
+      FAR FILE *stream;
+      int i;
+
+      /* Process each stream in the thread's stream list */
+
+      for (i = 0; i < 3; i++)
+        {
+          lib_fflush_unlocked(&list->sl_std[i]);
+        }
+
+      for (stream = list->sl_head; stream != NULL; stream = stream->fs_next)
+        {
+          /* If the stream is opened for writing, then flush all of
+           * the pending write data in the stream.
+           */
+
+          if ((stream->fs_oflags & O_WROK) != 0)
+            {
+              /* Flush the writable FILE */
+
+              ret = lib_fflush_unlocked(stream);
+              if (ret < 0)
+                {
+                  /* An error occurred during the flush AND/OR we were unable
+                   * to flush all of the buffered write data.  Remember the
+                   * last errcode.
+                   */
+
+                  lasterrno = ret;
+                }
+            }
+        }
+    }
+
+  /* If any flush failed, return the errorcode of the last failed flush */
+
+  return lasterrno;
+}
+
 int lib_flushall(FAR struct streamlist *list)
 {
   int lasterrno = OK;
@@ -52,7 +100,7 @@ int lib_flushall(FAR struct streamlist *list)
 
   /* Make sure that there are streams associated with this thread */
 
-  if (list)
+  if (list != NULL)
     {
       FAR FILE *stream;
       int i;
@@ -66,8 +114,7 @@ int lib_flushall(FAR struct streamlist *list)
           lib_fflush(&list->sl_std[i]);
         }
 
-      stream = list->sl_head;
-      for (; stream != NULL; stream = stream->fs_next)
+      for (stream = list->sl_head; stream != NULL; stream = stream->fs_next)
         {
           /* If the stream is opened for writing, then flush all of
            * the pending write data in the stream.
diff --git a/libs/libc/stdio/lib_putc.c b/libs/libc/stdio/lib_putc.c
index e3369c031c1..00162b72754 100644
--- a/libs/libc/stdio/lib_putc.c
+++ b/libs/libc/stdio/lib_putc.c
@@ -32,3 +32,8 @@ int putc(int c, FAR FILE *stream)
 {
   return fputc(c, stream);
 }
+
+int putc_unlocked(int c, FAR FILE *stream)
+{
+  return fputc_unlocked(c, stream);
+}
diff --git a/libs/libc/stdio/lib_putwchar.c b/libs/libc/stdio/lib_putwchar.c
index 6906cb82001..43911641c0d 100644
--- a/libs/libc/stdio/lib_putwchar.c
+++ b/libs/libc/stdio/lib_putwchar.c
@@ -51,13 +51,14 @@
  *
  ****************************************************************************/
 
-wint_t putwchar(wchar_t c)
+wint_t putwchar_unlocked(wchar_t c)
 {
 #ifdef CONFIG_FILE_STREAM
-  return fputwc(c, stdout);
+  return fputwc_unlocked(c, stdout);
 #else
   char mbc[MB_LEN_MAX];
   int l;
+
   l = wctomb(mbc, c);
   if (l < 0)
     {
@@ -67,3 +68,18 @@ wint_t putwchar(wchar_t c)
   return write(STDOUT_FILENO, mbc, l) == l ? c : WEOF;
 #endif
 }
+
+wint_t putwchar(wchar_t c)
+{
+  wint_t w;
+
+#ifdef CONFIG_FILE_STREAM
+  flockfile(stdout);
+#endif
+  w = putwchar_unlocked(c);
+#ifdef CONFIG_FILE_STREAM
+  funlockfile(stdout);
+#endif
+
+  return w;
+}