[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>
diff --git a/arch/um/include/line.h b/arch/um/include/line.h
index 5f232ae8..b79643e 100644
--- a/arch/um/include/line.h
+++ b/arch/um/include/line.h
@@ -11,6 +11,7 @@
#include "linux/tty.h"
#include "linux/interrupt.h"
#include "linux/spinlock.h"
+#include "linux/mutex.h"
#include "chan_user.h"
#include "mconsole_kern.h"
@@ -32,15 +33,17 @@
struct line {
struct tty_struct *tty;
+ spinlock_t count_lock;
+ int valid;
+
+ struct mutex open_mutex;
char *init_str;
int init_pri;
struct list_head chan_list;
- int valid;
- int count;
- int throttled;
+
/*This lock is actually, mostly, local to*/
spinlock_t lock;
-
+ int throttled;
/* Yes, this is a real circular buffer.
* XXX: And this should become a struct kfifo!
*
@@ -57,7 +60,8 @@
};
#define LINE_INIT(str, d) \
- { .init_str = str, \
+ { .count_lock = SPIN_LOCK_UNLOCKED, \
+ .init_str = str, \
.init_pri = INIT_STATIC, \
.valid = 1, \
.lock = SPIN_LOCK_UNLOCKED, \