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 <[EMAIL PROTECTED]>
--
arch/um/drivers/line.c | 188 ++++++++++++++++++++++++++--------------
arch/um/drivers/stdio_console.c | 6 -
arch/um/include/line.h | 14 +-
3 files changed, 135 insertions(+), 73 deletions(-)
Index: linux-2.6.18-mm/arch/um/drivers/line.c
===================================================================
--- linux-2.6.18-mm.orig/arch/um/drivers/line.c 2006-12-29 15:12:45.000000000
-0500
+++ linux-2.6.18-mm/arch/um/drivers/line.c 2006-12-29 17:26:26.000000000
-0500
@@ -191,7 +191,6 @@ void line_flush_buffer(struct tty_struct
/*XXX: copied from line_write, verify if it is correct!*/
if(tty->stopped)
return;
- //return 0;
spin_lock_irqsave(&line->lock, flags);
err = flush_buffer(line);
@@ -421,42 +420,84 @@ int line_setup_irq(int fd, int input, in
return err;
}
+/* Normally, a driver like this can rely mostly on the tty layer
+ * locking, particularly when it comes to the driver structure.
+ * However, in this case, mconsole requests can come in "from the
+ * side", and race with opens and closes.
+ *
+ * The problem comes from line_setup not wanting to sleep if
+ * the device is open or being opened. This can happen because the
+ * first opener of a device is responsible for setting it up on the
+ * host, and that can sleep. The open of a port device will sleep
+ * until someone telnets to it.
+ *
+ * The obvious solution of putting everything under a mutex fails
+ * because then trying (and failing) to change the configuration of an
+ * open(ing) device will block until the open finishes. The right
+ * thing to happen is for it to fail immediately.
+ *
+ * We can put the opening (and closing) of the host device under a
+ * separate lock, but that has to be taken before the count lock is
+ * released. Otherwise, you open a window in which another open can
+ * come through and assume that the host side is opened and working.
+ *
+ * So, if the tty count is one, open will take the open mutex
+ * inside the count lock. Otherwise, it just returns. This will sleep
+ * if the last close is pending, and will block a setup or get_config,
+ * but that should not last long.
+ *
+ * So, what we end up with is that open and close take the count lock.
+ * If the first open or last close are happening, then the open mutex
+ * is taken inside the count lock and the host opening or closing is done.
+ *
+ * setup and get_config only take the count lock. setup modifies the
+ * device configuration only if the open count is zero. Arbitrarily
+ * long blocking of setup doesn't happen because something would have to be
+ * waiting for an open to happen. However, a second open with
+ * tty->count == 1 can't happen, and a close can't happen until the open
+ * had finished.
+ *
+ * We can't maintain our own count here because the tty layer doesn't
+ * match opens and closes. It will call close if an open failed, and
+ * a tty hangup will result in excess closes. So, we rely on
+ * tty->count instead. It is one on both the first open and last close.
+ */
+
int line_open(struct line *lines, struct tty_struct *tty)
{
- struct line *line;
+ struct line *line = &lines[tty->index];
int err = -ENODEV;
- line = &lines[tty->index];
- tty->driver_data = line;
+ spin_lock(&line->count_lock);
+ if(!line->valid)
+ goto out_unlock;
+
+ err = 0;
+ if(tty->count > 1)
+ goto out_unlock;
- /* The IRQ which takes this lock is not yet enabled and won't be run
- * before the end, so we don't need to use spin_lock_irq.*/
- spin_lock(&line->lock);
+ mutex_lock(&line->open_mutex);
+ spin_unlock(&line->count_lock);
tty->driver_data = line;
line->tty = tty;
- if(!line->valid)
- goto out;
- if(tty->count == 1){
- /* Here the device is opened, if necessary, and interrupt
- * is registered.
- */
- enable_chan(line);
- INIT_DELAYED_WORK(&line->task, line_timer_cb);
-
- if(!line->sigio){
- chan_enable_winch(&line->chan_list, tty);
- line->sigio = 1;
- }
+ enable_chan(line);
+ INIT_DELAYED_WORK(&line->task, line_timer_cb);
- chan_window_size(&line->chan_list, &tty->winsize.ws_row,
- &tty->winsize.ws_col);
+ if(!line->sigio){
+ chan_enable_winch(&line->chan_list, tty);
+ line->sigio = 1;
}
- err = 0;
-out:
- spin_unlock(&line->lock);
+ chan_window_size(&line->chan_list, &tty->winsize.ws_row,
+ &tty->winsize.ws_col);
+
+ mutex_unlock(&line->open_mutex);
+ return err;
+
+out_unlock:
+ spin_unlock(&line->count_lock);
return err;
}
@@ -466,25 +507,38 @@ void line_close(struct tty_struct *tty,
{
struct line *line = tty->driver_data;
- /* XXX: I assume this should be called in process context, not with
- * interrupts disabled!
- */
- spin_lock_irq(&line->lock);
+ /* If line_open fails (and tty->driver_data is never set),
+ * tty_open will call line_close. So just return in this case.
+ */
+ if(line == NULL)
+ return;
/* We ignore the error anyway! */
flush_buffer(line);
- if(tty->count == 1){
- line->tty = NULL;
- tty->driver_data = NULL;
-
- if(line->sigio){
- unregister_winch(tty);
- line->sigio = 0;
- }
+ spin_lock(&line->count_lock);
+ if(!line->valid)
+ goto out_unlock;
+
+ if(tty->count > 1)
+ goto out_unlock;
+
+ mutex_lock(&line->open_mutex);
+ spin_unlock(&line->count_lock);
+
+ line->tty = NULL;
+ tty->driver_data = NULL;
+
+ if(line->sigio){
+ unregister_winch(tty);
+ line->sigio = 0;
}
- spin_unlock_irq(&line->lock);
+ mutex_unlock(&line->open_mutex);
+ return;
+
+out_unlock:
+ spin_unlock(&line->count_lock);
}
void close_lines(struct line *lines, int nlines)
@@ -495,6 +549,30 @@ void close_lines(struct line *lines, int
close_chan(&lines[i].chan_list, 0);
}
+static void setup_one_line(struct line *lines, int n, char *init, int
init_prio)
+{
+ struct line *line = &lines[n];
+
+ spin_lock(&line->count_lock);
+
+ if(line->tty != NULL){
+ printk("line_setup - device %d is open\n", n);
+ goto out;
+ }
+
+ if (line->init_pri <= init_prio){
+ line->init_pri = init_prio;
+ if (!strcmp(init, "none"))
+ line->valid = 0;
+ else {
+ line->init_str = init;
+ line->valid = 1;
+ }
+ }
+out:
+ spin_unlock(&line->count_lock);
+}
+
/* Common setup code for both startup command line and mconsole initialization.
* @lines contains the array (of size @num) to modify;
* @init is the setup string;
@@ -526,32 +604,11 @@ int line_setup(struct line *lines, unsig
n, num - 1);
return 0;
}
- else if (n >= 0){
- if (lines[n].tty != NULL) {
- printk("line_setup - device %d is open\n", n);
- return 0;
- }
- if (lines[n].init_pri <= INIT_ONE){
- lines[n].init_pri = INIT_ONE;
- if (!strcmp(init, "none"))
- lines[n].valid = 0;
- else {
- lines[n].init_str = init;
- lines[n].valid = 1;
- }
- }
- }
+ else if (n >= 0)
+ setup_one_line(lines, n, init, INIT_ONE);
else {
- for(i = 0; i < num; i++){
- if(lines[i].init_pri <= INIT_ALL){
- lines[i].init_pri = INIT_ALL;
- if(!strcmp(init, "none")) lines[i].valid = 0;
- else {
- lines[i].init_str = init;
- lines[i].valid = 1;
- }
- }
- }
+ for(i = 0; i < num; i++)
+ setup_one_line(lines, i, init, INIT_ALL);
}
return n == -1 ? num : n;
}
@@ -602,13 +659,13 @@ int line_get_config(char *name, struct l
line = &lines[dev];
- spin_lock(&line->lock);
+ spin_lock(&line->count_lock);
if(!line->valid)
CONFIG_CHUNK(str, size, n, "none", 1);
else if(line->tty == NULL)
CONFIG_CHUNK(str, size, n, line->init_str, 1);
else n = chan_config_string(&line->chan_list, str, size, error_out);
- spin_unlock(&line->lock);
+ spin_unlock(&line->count_lock);
return n;
}
@@ -688,6 +745,7 @@ void lines_init(struct line *lines, int
for(i = 0; i < nlines; i++){
line = &lines[i];
INIT_LIST_HEAD(&line->chan_list);
+ mutex_init(&line->open_mutex);
if(line->init_str == NULL)
continue;
Index: linux-2.6.18-mm/arch/um/drivers/stdio_console.c
===================================================================
--- linux-2.6.18-mm.orig/arch/um/drivers/stdio_console.c 2006-12-29
15:12:43.000000000 -0500
+++ linux-2.6.18-mm/arch/um/drivers/stdio_console.c 2006-12-29
17:26:26.000000000 -0500
@@ -83,9 +83,9 @@ static struct lines console_lines = LINE
/* 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)
{
Index: linux-2.6.18-mm/arch/um/include/line.h
===================================================================
--- linux-2.6.18-mm.orig/arch/um/include/line.h 2006-12-29 15:12:43.000000000
-0500
+++ linux-2.6.18-mm/arch/um/include/line.h 2006-12-29 17:26:26.000000000
-0500
@@ -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_driver {
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 @@ struct line {
};
#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, \
-
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