[PATCH] convert fs/9p/ to mutexes, fix locking bugs

Convert fs/9p/mux.c from semaphore to mutex.

NOTE: fixed locking bugs in the process - the code was using semaphores
the other way around.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Eric Van Hensbergen <ericvh@ericvh.myip.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/9p/mux.c

@@ -31,6 +31,7 @@
 #include <linux/poll.h>
 #include <linux/kthread.h>
 #include <linux/idr.h>
+#include <linux/mutex.h>
 
 #include "debug.h"
 #include "v9fs.h"
@@ -110,7 +111,7 @@ static void v9fs_pollwait(struct file *filp, wait_queue_head_t * wait_address,
 static u16 v9fs_mux_get_tag(struct v9fs_mux_data *);
 static void v9fs_mux_put_tag(struct v9fs_mux_data *, u16);
 
-static DECLARE_MUTEX(v9fs_mux_task_lock);
+static DEFINE_MUTEX(v9fs_mux_task_lock);
 static struct workqueue_struct *v9fs_mux_wq;
 
 static int v9fs_mux_num;
@@ -166,7 +167,7 @@ static int v9fs_mux_poll_start(struct v9fs_mux_data *m)
 
 	dprintk(DEBUG_MUX, "mux %p muxnum %d procnum %d\n", m, v9fs_mux_num,
 		v9fs_mux_poll_task_num);
-	up(&v9fs_mux_task_lock);
+	mutex_lock(&v9fs_mux_task_lock);
 
 	n = v9fs_mux_calc_poll_procs(v9fs_mux_num + 1);
 	if (n > v9fs_mux_poll_task_num) {
@@ -225,7 +226,7 @@ static int v9fs_mux_poll_start(struct v9fs_mux_data *m)
 	}
 
 	v9fs_mux_num++;
-	down(&v9fs_mux_task_lock);
+	mutex_unlock(&v9fs_mux_task_lock);
 
 	return 0;
 }
@@ -235,7 +236,7 @@ static void v9fs_mux_poll_stop(struct v9fs_mux_data *m)
 	int i;
 	struct v9fs_mux_poll_task *vpt;
 
-	up(&v9fs_mux_task_lock);
+	mutex_lock(&v9fs_mux_task_lock);
 	vpt = m->poll_task;
 	list_del(&m->mux_list);
 	for(i = 0; i < ARRAY_SIZE(m->poll_waddr); i++) {
@@ -252,7 +253,7 @@ static void v9fs_mux_poll_stop(struct v9fs_mux_data *m)
 		v9fs_mux_poll_task_num--;
 	}
 	v9fs_mux_num--;
-	down(&v9fs_mux_task_lock);
+	mutex_unlock(&v9fs_mux_task_lock);
 }
 
 /**