[PATCH] uml: console locking fixes

Clean up the console driver locking.  There are various problems here,
including sleeping under a spinlock and spinlock recursion, some of which are
fixed here.  This patch deals with the locking involved with opens and closes.
 The problem is that an mconsole request to change a console's configuration
can race with an open.  Changing a configuration should only be done when a
console isn't opened.  Also, an open must be looking at a stable
configuration.  In addition, a get configuration request must observe the same
locking since it must also see a stable configuration.  With the old locking,
it was possible for this to hang indefinitely in some cases because open would
block for a long time waiting for a connection from the host while holding the
lock needed by the mconsole request.

As explained in the long comment, this is fixed by adding a spinlock for the
use count and configuration and a mutex for the actual open and close.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/arch/um/drivers/stdio_console.c b/arch/um/drivers/stdio_console.c
index 7a4897e..9b2dd0b 100644
--- a/arch/um/drivers/stdio_console.c
+++ b/arch/um/drivers/stdio_console.c
@@ -83,9 +83,9 @@ static struct lines console_lines = LINES_INIT(MAX_TTYS);
 /* The array is initialized by line_init, which is an initcall.  The 
  * individual elements are protected by individual semaphores.
  */
-struct line vts[MAX_TTYS] = { LINE_INIT(CONFIG_CON_ZERO_CHAN, &driver),
-			      [ 1 ... MAX_TTYS - 1 ] =
-			      LINE_INIT(CONFIG_CON_CHAN, &driver) };
+static struct line vts[MAX_TTYS] = { LINE_INIT(CONFIG_CON_ZERO_CHAN, &driver),
+				     [ 1 ... MAX_TTYS - 1 ] =
+				     LINE_INIT(CONFIG_CON_CHAN, &driver) };
 
 static int con_config(char *str)
 {