[PATCH] uml: locking documentation

Some locking documentation and a cleanup.  uml_exitcode is copied into a local
before sprintf sees it, in case sprintf does anything non-atomic with it.

The rest are comments about why certain globals don't need any kind of
locking.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 14 insertions, 2 deletions

diff --git a/arch/um/drivers/null.c b/arch/um/drivers/null.c
index 3683ed44315d..9016c68beee8 100644
--- a/arch/um/drivers/null.c
+++ b/arch/um/drivers/null.c
@@ -8,6 +8,7 @@
 #include "chan_user.h"
 #include "os.h"
 
+/* This address is used only as a unique identifer */
 static int null_chan;
 
 static void *null_init(char *str, int device, const struct chan_opts *opts)
diff --git a/arch/um/drivers/random.c b/arch/um/drivers/random.c
index ae9909415b9c..73b2bdd6d2d3 100644
--- a/arch/um/drivers/random.c
+++ b/arch/um/drivers/random.c
@@ -20,6 +20,10 @@
 
 #define RNG_MISCDEV_MINOR               183 /* official */
 
+/* Changed at init time, in the non-modular case, and at module load
+ * time, in the module case.  Presumably, the module subsystem
+ * protects against a module being loaded twice at the same time.
+ */
 static int random_fd = -1;
 
 static int rng_dev_open (struct inode *inode, struct file *filp)
diff --git a/arch/um/drivers/stderr_console.c b/arch/um/drivers/stderr_console.c
index 6d2cf32a9e8f..911539293871 100644
--- a/arch/um/drivers/stderr_console.c
+++ b/arch/um/drivers/stderr_console.c
@@ -9,6 +9,8 @@
 /*
  * Don't register by default -- as this registeres very early in the
  * boot process it becomes the default console.
+ *
+ * Initialized at init time.
  */
 static int use_stderr_console = 0;
 
diff --git a/arch/um/drivers/stdio_console.c b/arch/um/drivers/stdio_console.c
index 5e44adb07051..e4bfcfe8550b 100644
--- a/arch/um/drivers/stdio_console.c
+++ b/arch/um/drivers/stdio_console.c
@@ -108,6 +108,7 @@ static int con_open(struct tty_struct *tty, struct file *filp)
         return line_open(vts, tty);
 }
 
+/* Set in an initcall, checked in an exitcall */
 static int con_init_done = 0;
 
 static const struct tty_operations console_ops = {
diff --git a/arch/um/kernel/exitcode.c b/arch/um/kernel/exitcode.c
index d21ebad666b4..8b7f2cdedf94 100644
--- a/arch/um/kernel/exitcode.c
+++ b/arch/um/kernel/exitcode.c
@@ -16,9 +16,13 @@ int uml_exitcode = 0;
 static int read_proc_exitcode(char *page, char **start, off_t off,
                               int count, int *eof, void *data)
 {
-        int len;
+        int len, val;
 
-        len = sprintf(page, "%d\n", uml_exitcode);
+        /* Save uml_exitcode in a local so that we don't need to guarantee
+         * that sprintf accesses it atomically.
+         */
+        val = uml_exitcode;
+        len = sprintf(page, "%d\n", val);
         len -= off;
         if(len <= off+count) *eof = 1;
         *start = page + off;