tty,vcs removing con_buf/conf_buf_mtx

seems there's no longer need for using con_buf/conf_buf_mtx
as vcs_read/vcs_write buffer for user's data.

The do_con_write function, that was the other user of this,
is currently using its own kmalloc-ed buffer.

Not sure when this got changed, as I was able to find this code
in 2.6.9, but it's already gone as far as current git history
goes - 2.6.12-rc2.

AFAICS there's a behaviour change with the current change.
The lseek is not completely mutually exclusive with the
vcs_read/vcs_write - the file->f_pos might get updated
via lseek callback during the vcs_read/vcs_write processing.

I tried to find out if the prefered behaviour is to keep
this in sync within read/write/lseek functions, but I did
not find any pattern on different places.

I guess if user end up calling write/lseek from different
threads she should know what she's doing. If needed we
could use dedicated fd mutex/buffer.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 52 insertions, 58 deletions

diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index 3c27c4bc6040..7b3bfbe2e6de 100644
--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -28,7 +28,6 @@
 #include <linux/interrupt.h>
 #include <linux/mm.h>
 #include <linux/init.h>
-#include <linux/mutex.h>
 #include <linux/vt_kern.h>
 #include <linux/selection.h>
 #include <linux/kbd_kern.h>
@@ -51,6 +50,8 @@
 #undef addr
 #define HEADER_SIZE     4
 
+#define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 256 : PAGE_SIZE)
+
 struct vcs_poll_data {
         struct notifier_block notifier;
         unsigned int cons_num;
@@ -131,21 +132,45 @@ vcs_poll_data_get(struct file *file)
         return poll;
 }
 
+/*
+ * Returns VC for inode.
+ * Must be called with console_lock.
+ */
+static struct vc_data*
+vcs_vc(struct inode *inode, int *viewed)
+{
+        unsigned int currcons = iminor(inode) & 127;
+
+        WARN_CONSOLE_UNLOCKED();
+
+        if (currcons == 0) {
+                currcons = fg_console;
+                if (viewed)
+                        *viewed = 1;
+        } else {
+                currcons--;
+                if (viewed)
+                        *viewed = 0;
+        }
+        return vc_cons[currcons].d;
+}
+
+/*
+ * Returns size for VC carried by inode.
+ * Must be called with console_lock.
+ */
 static int
 vcs_size(struct inode *inode)
 {
         int size;
         int minor = iminor(inode);
-        int currcons = minor & 127;
         struct vc_data *vc;
 
-        if (currcons == 0)
-                currcons = fg_console;
-        else
-                currcons--;
-        if (!vc_cons_allocated(currcons))
+        WARN_CONSOLE_UNLOCKED();
+
+        vc = vcs_vc(inode, NULL);
+        if (!vc)
                 return -ENXIO;
-        vc = vc_cons[currcons].d;
 
         size = vc->vc_rows * vc->vc_cols;
 
@@ -158,17 +183,13 @@ static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
 {
         int size;
 
-        mutex_lock(&con_buf_mtx);
         console_lock();
         size = vcs_size(file->f_path.dentry->d_inode);
         console_unlock();
-        if (size < 0) {
-                mutex_unlock(&con_buf_mtx);
+        if (size < 0)
                 return size;
-        }
         switch (orig) {
                 default:
-                        mutex_unlock(&con_buf_mtx);
                         return -EINVAL;
                 case 2:
                         offset += size;
@@ -179,11 +200,9 @@ static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
                         break;
         }
         if (offset < 0 || offset > size) {
-                mutex_unlock(&con_buf_mtx);
                 return -EINVAL;
         }
         file->f_pos = offset;
-        mutex_unlock(&con_buf_mtx);
         return file->f_pos;
 }
 
@@ -196,12 +215,15 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
         struct vc_data *vc;
         struct vcs_poll_data *poll;
         long pos;
-        long viewed, attr, read;
-        int col, maxcol;
+        long attr, read;
+        int col, maxcol, viewed;
         unsigned short *org = NULL;
         ssize_t ret;
+        char *con_buf;
 
-        mutex_lock(&con_buf_mtx);
+        con_buf = (char *) __get_free_page(GFP_KERNEL);
+        if (!con_buf)
+                return -ENOMEM;
 
         pos = *ppos;
 
@@ -211,18 +233,10 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
         console_lock();
 
         attr = (currcons & 128);
-        currcons = (currcons & 127);
-        if (currcons == 0) {
-                currcons = fg_console;
-                viewed = 1;
-        } else {
-                currcons--;
-                viewed = 0;
-        }
         ret = -ENXIO;
-        if (!vc_cons_allocated(currcons))
+        vc = vcs_vc(inode, &viewed);
+        if (!vc)
                 goto unlock_out;
-        vc = vc_cons[currcons].d;
 
         ret = -EINVAL;
         if (pos < 0)
@@ -367,7 +381,7 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
                 ret = read;
 unlock_out:
         console_unlock();
-        mutex_unlock(&con_buf_mtx);
+        free_page((unsigned long) con_buf);
         return ret;
 }
 
@@ -378,13 +392,16 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
         unsigned int currcons = iminor(inode);
         struct vc_data *vc;
         long pos;
-        long viewed, attr, size, written;
+        long attr, size, written;
         char *con_buf0;
-        int col, maxcol;
+        int col, maxcol, viewed;
         u16 *org0 = NULL, *org = NULL;
         size_t ret;
+        char *con_buf;
 
-        mutex_lock(&con_buf_mtx);
+        con_buf = (char *) __get_free_page(GFP_KERNEL);
+        if (!con_buf)
+                return -ENOMEM;
 
         pos = *ppos;
 
@@ -394,19 +411,10 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
         console_lock();
 
         attr = (currcons & 128);
-        currcons = (currcons & 127);
-
-        if (currcons == 0) {
-                currcons = fg_console;
-                viewed = 1;
-        } else {
-                currcons--;
-                viewed = 0;
-        }
         ret = -ENXIO;
-        if (!vc_cons_allocated(currcons))
+        vc = vcs_vc(inode, &viewed);
+        if (!vc)
                 goto unlock_out;
-        vc = vc_cons[currcons].d;
 
         size = vcs_size(inode);
         ret = -EINVAL;
@@ -561,9 +569,7 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 
 unlock_out:
         console_unlock();
-
-        mutex_unlock(&con_buf_mtx);
-
+        free_page((unsigned long) con_buf);
         return ret;
 }
 
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index d5669ff72df4..798df6f89110 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2068,18 +2068,6 @@ static void do_con_trol(struct tty_struct *tty, struct vc_data *vc, int c)
         }
 }
 
-/* This is a temporary buffer used to prepare a tty console write
- * so that we can easily avoid touching user space while holding the
- * console spinlock.  It is allocated in con_init and is shared by
- * this code and the vc_screen read/write tty calls.
- *
- * We have to allocate this statically in the kernel data section
- * since console_init (and thus con_init) are called before any
- * kernel memory allocation is available.
- */
-char con_buf[CON_BUF_SIZE];
-DEFINE_MUTEX(con_buf_mtx);
-
 /* is_double_width() is based on the wcwidth() implementation by
  * Markus Kuhn -- 2007-05-26 (Unicode 5.0)
  * Latest version: http://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c