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[PATCH] uml: console locking fixes

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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>
This commit is contained in:
Jeff Dike
2007-02-10 01:43:52 -08:00
committed by Linus Torvalds
parent 5cf885d01f
commit d79a580936
3 changed files with 134 additions and 72 deletions
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6
arch/um/drivers/stdio_console.c
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@@ -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)
{