um: convert count_lock to mutex, fix a race in line_open()

If two processes are opening the same line, the second to get
into line_open() will decide that it doesn't need to do anything
(correctly) or wait for anything.  The latter, unfortunately,
is incorrect - the first opener might not be through yet.  We
need to have exclusion covering the entire line_init(), including
the blocking parts.  Moreover, the next patch will need to
widen the exclusion on mconsole side of things, also including
the blocking bits, so let's just convert that sucker to mutex...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

4 files changed, 12 insertions, 20 deletions

diff --git a/arch/um/drivers/line.c b/arch/um/drivers/line.c
index 3eea99e98a11..dc7e216df6a5 100644
--- a/arch/um/drivers/line.c
+++ b/arch/um/drivers/line.c
@@ -409,7 +409,7 @@ int line_open(struct line *lines, struct tty_struct *tty)
         struct line *line = &lines[tty->index];
         int err = -ENODEV;
 
-        spin_lock(&line->count_lock);
+        mutex_lock(&line->count_lock);
         if (!line->valid)
                 goto out_unlock;
 
@@ -421,10 +421,9 @@ int line_open(struct line *lines, struct tty_struct *tty)
         tty->driver_data = line;
         line->tty = tty;
 
-        spin_unlock(&line->count_lock);
         err = enable_chan(line);
         if (err) /* line_close() will be called by our caller */
-                return err;
+                goto out_unlock;
 
         INIT_DELAYED_WORK(&line->task, line_timer_cb);
 
@@ -435,11 +434,8 @@ int line_open(struct line *lines, struct tty_struct *tty)
 
         chan_window_size(&line->chan_list, &tty->winsize.ws_row,
                          &tty->winsize.ws_col);
-
-        return 0;
-
 out_unlock:
-        spin_unlock(&line->count_lock);
+        mutex_unlock(&line->count_lock);
         return err;
 }
 
@@ -459,7 +455,7 @@ void line_close(struct tty_struct *tty, struct file * filp)
         /* We ignore the error anyway! */
         flush_buffer(line);
 
-        spin_lock(&line->count_lock);
+        mutex_lock(&line->count_lock);
         BUG_ON(!line->valid);
 
         if (--line->count)
@@ -468,17 +464,13 @@ void line_close(struct tty_struct *tty, struct file * filp)
         line->tty = NULL;
         tty->driver_data = NULL;
 
-        spin_unlock(&line->count_lock);
-
         if (line->sigio) {
                 unregister_winch(tty);
                 line->sigio = 0;
         }
 
-        return;
-
 out_unlock:
-        spin_unlock(&line->count_lock);
+        mutex_unlock(&line->count_lock);
 }
 
 void close_lines(struct line *lines, int nlines)
@@ -495,7 +487,7 @@ static int setup_one_line(struct line *lines, int n, char *init,
         struct line *line = &lines[n];
         int err = -EINVAL;
 
-        spin_lock(&line->count_lock);
+        mutex_lock(&line->count_lock);
 
         if (line->count) {
                 *error_out = "Device is already open";
@@ -510,7 +502,7 @@ static int setup_one_line(struct line *lines, int n, char *init,
         }
         err = 0;
 out:
-        spin_unlock(&line->count_lock);
+        mutex_unlock(&line->count_lock);
         return err;
 }
 
@@ -609,13 +601,13 @@ int line_get_config(char *name, struct line *lines, unsigned int num, char *str,
 
         line = &lines[dev];
 
-        spin_lock(&line->count_lock);
+        mutex_lock(&line->count_lock);
         if (!line->valid)
                 CONFIG_CHUNK(str, size, n, "none", 1);
         else if (line->tty == NULL)
                 CONFIG_CHUNK(str, size, n, line->init_str, 1);
         else n = chan_config_string(&line->chan_list, str, size, error_out);
-        spin_unlock(&line->count_lock);
+        mutex_unlock(&line->count_lock);
 
         return n;
 }
diff --git a/arch/um/drivers/line.h b/arch/um/drivers/line.h
index 0c4dadf5e03e..471f477b271e 100644
--- a/arch/um/drivers/line.h
+++ b/arch/um/drivers/line.h
@@ -32,7 +32,7 @@ struct line_driver {
 
 struct line {
         struct tty_struct *tty;
-        spinlock_t count_lock;
+        struct mutex count_lock;
         unsigned long count;
         int valid;
 
diff --git a/arch/um/drivers/ssl.c b/arch/um/drivers/ssl.c
index 445288ff0650..23cffd6d85af 100644
--- a/arch/um/drivers/ssl.c
+++ b/arch/um/drivers/ssl.c
@@ -201,7 +201,7 @@ static int ssl_init(void)
                         serial_lines[i].valid = 1;
                 }
                 spin_lock_init(&serial_lines[i].lock);
-                spin_lock_init(&serial_lines[i].count_lock);
+                mutex_init(&serial_lines[i].count_lock);
                 serial_lines[i].driver = &driver;
         }
         ssl_driver = register_lines(&driver, &ssl_ops, serial_lines,
diff --git a/arch/um/drivers/stdio_console.c b/arch/um/drivers/stdio_console.c
index 6d244f470968..f8d4325b28b7 100644
--- a/arch/um/drivers/stdio_console.c
+++ b/arch/um/drivers/stdio_console.c
@@ -173,7 +173,7 @@ static int stdio_init(void)
                         vts[i].valid = 1;
                 }
                 spin_lock_init(&vts[i].lock);
-                spin_lock_init(&vts[i].count_lock);
+                mutex_init(&vts[i].count_lock);
                 vts[i].driver = &driver;
         }
         console_driver = register_lines(&driver, &console_ops, vts,