mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 10:49:33 +00:00
[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>
This commit is contained in:
parent
5cf885d01f
commit
d79a580936
3 changed files with 134 additions and 72 deletions
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@ -191,7 +191,6 @@ void line_flush_buffer(struct tty_struct *tty)
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/*XXX: copied from line_write, verify if it is correct!*/
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if(tty->stopped)
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return;
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//return 0;
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spin_lock_irqsave(&line->lock, flags);
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err = flush_buffer(line);
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@ -421,42 +420,84 @@ int line_setup_irq(int fd, int input, int output, struct line *line, void *data)
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return err;
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}
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/* Normally, a driver like this can rely mostly on the tty layer
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* locking, particularly when it comes to the driver structure.
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* However, in this case, mconsole requests can come in "from the
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* side", and race with opens and closes.
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*
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* The problem comes from line_setup not wanting to sleep if
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* the device is open or being opened. This can happen because the
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* first opener of a device is responsible for setting it up on the
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* host, and that can sleep. The open of a port device will sleep
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* until someone telnets to it.
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*
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* The obvious solution of putting everything under a mutex fails
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* because then trying (and failing) to change the configuration of an
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* open(ing) device will block until the open finishes. The right
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* thing to happen is for it to fail immediately.
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*
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* We can put the opening (and closing) of the host device under a
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* separate lock, but that has to be taken before the count lock is
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* released. Otherwise, you open a window in which another open can
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* come through and assume that the host side is opened and working.
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*
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* So, if the tty count is one, open will take the open mutex
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* inside the count lock. Otherwise, it just returns. This will sleep
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* if the last close is pending, and will block a setup or get_config,
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* but that should not last long.
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*
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* So, what we end up with is that open and close take the count lock.
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* If the first open or last close are happening, then the open mutex
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* is taken inside the count lock and the host opening or closing is done.
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*
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* setup and get_config only take the count lock. setup modifies the
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* device configuration only if the open count is zero. Arbitrarily
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* long blocking of setup doesn't happen because something would have to be
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* waiting for an open to happen. However, a second open with
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* tty->count == 1 can't happen, and a close can't happen until the open
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* had finished.
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*
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* We can't maintain our own count here because the tty layer doesn't
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* match opens and closes. It will call close if an open failed, and
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* a tty hangup will result in excess closes. So, we rely on
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* tty->count instead. It is one on both the first open and last close.
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*/
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int line_open(struct line *lines, struct tty_struct *tty)
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{
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struct line *line;
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struct line *line = &lines[tty->index];
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int err = -ENODEV;
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line = &lines[tty->index];
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tty->driver_data = line;
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spin_lock(&line->count_lock);
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if(!line->valid)
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goto out_unlock;
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/* The IRQ which takes this lock is not yet enabled and won't be run
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* before the end, so we don't need to use spin_lock_irq.*/
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spin_lock(&line->lock);
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err = 0;
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if(tty->count > 1)
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goto out_unlock;
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mutex_lock(&line->open_mutex);
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spin_unlock(&line->count_lock);
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tty->driver_data = line;
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line->tty = tty;
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if(!line->valid)
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goto out;
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if(tty->count == 1){
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/* Here the device is opened, if necessary, and interrupt
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* is registered.
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*/
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enable_chan(line);
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INIT_DELAYED_WORK(&line->task, line_timer_cb);
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enable_chan(line);
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INIT_DELAYED_WORK(&line->task, line_timer_cb);
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if(!line->sigio){
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chan_enable_winch(&line->chan_list, tty);
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line->sigio = 1;
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}
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chan_window_size(&line->chan_list, &tty->winsize.ws_row,
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&tty->winsize.ws_col);
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if(!line->sigio){
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chan_enable_winch(&line->chan_list, tty);
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line->sigio = 1;
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}
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err = 0;
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out:
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spin_unlock(&line->lock);
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chan_window_size(&line->chan_list, &tty->winsize.ws_row,
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&tty->winsize.ws_col);
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mutex_unlock(&line->open_mutex);
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return err;
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out_unlock:
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spin_unlock(&line->count_lock);
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return err;
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}
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@ -466,25 +507,38 @@ void line_close(struct tty_struct *tty, struct file * filp)
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{
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struct line *line = tty->driver_data;
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/* XXX: I assume this should be called in process context, not with
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* interrupts disabled!
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*/
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spin_lock_irq(&line->lock);
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/* If line_open fails (and tty->driver_data is never set),
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* tty_open will call line_close. So just return in this case.
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*/
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if(line == NULL)
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return;
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/* We ignore the error anyway! */
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flush_buffer(line);
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if(tty->count == 1){
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line->tty = NULL;
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tty->driver_data = NULL;
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spin_lock(&line->count_lock);
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if(!line->valid)
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goto out_unlock;
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if(line->sigio){
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unregister_winch(tty);
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line->sigio = 0;
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}
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if(tty->count > 1)
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goto out_unlock;
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mutex_lock(&line->open_mutex);
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spin_unlock(&line->count_lock);
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line->tty = NULL;
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tty->driver_data = NULL;
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if(line->sigio){
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unregister_winch(tty);
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line->sigio = 0;
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}
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spin_unlock_irq(&line->lock);
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mutex_unlock(&line->open_mutex);
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return;
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out_unlock:
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spin_unlock(&line->count_lock);
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}
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void close_lines(struct line *lines, int nlines)
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@ -495,6 +549,30 @@ void close_lines(struct line *lines, int nlines)
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close_chan(&lines[i].chan_list, 0);
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}
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static void setup_one_line(struct line *lines, int n, char *init, int init_prio)
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{
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struct line *line = &lines[n];
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spin_lock(&line->count_lock);
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if(line->tty != NULL){
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printk("line_setup - device %d is open\n", n);
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goto out;
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}
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if (line->init_pri <= init_prio){
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line->init_pri = init_prio;
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if (!strcmp(init, "none"))
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line->valid = 0;
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else {
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line->init_str = init;
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line->valid = 1;
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}
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}
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out:
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spin_unlock(&line->count_lock);
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}
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/* Common setup code for both startup command line and mconsole initialization.
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* @lines contains the array (of size @num) to modify;
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* @init is the setup string;
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@ -526,32 +604,11 @@ int line_setup(struct line *lines, unsigned int num, char *init)
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n, num - 1);
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return 0;
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}
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else if (n >= 0){
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if (lines[n].tty != NULL) {
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printk("line_setup - device %d is open\n", n);
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return 0;
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}
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if (lines[n].init_pri <= INIT_ONE){
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lines[n].init_pri = INIT_ONE;
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if (!strcmp(init, "none"))
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lines[n].valid = 0;
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else {
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lines[n].init_str = init;
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lines[n].valid = 1;
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}
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}
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}
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else if (n >= 0)
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setup_one_line(lines, n, init, INIT_ONE);
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else {
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for(i = 0; i < num; i++){
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if(lines[i].init_pri <= INIT_ALL){
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lines[i].init_pri = INIT_ALL;
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if(!strcmp(init, "none")) lines[i].valid = 0;
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else {
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lines[i].init_str = init;
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lines[i].valid = 1;
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}
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}
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}
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for(i = 0; i < num; i++)
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setup_one_line(lines, i, init, INIT_ALL);
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}
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return n == -1 ? num : n;
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}
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@ -602,13 +659,13 @@ int line_get_config(char *name, struct line *lines, unsigned int num, char *str,
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line = &lines[dev];
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spin_lock(&line->lock);
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spin_lock(&line->count_lock);
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if(!line->valid)
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CONFIG_CHUNK(str, size, n, "none", 1);
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else if(line->tty == NULL)
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CONFIG_CHUNK(str, size, n, line->init_str, 1);
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else n = chan_config_string(&line->chan_list, str, size, error_out);
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spin_unlock(&line->lock);
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spin_unlock(&line->count_lock);
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return n;
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}
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for(i = 0; i < nlines; i++){
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line = &lines[i];
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INIT_LIST_HEAD(&line->chan_list);
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mutex_init(&line->open_mutex);
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if(line->init_str == NULL)
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continue;
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@ -83,9 +83,9 @@ static struct lines console_lines = LINES_INIT(MAX_TTYS);
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/* The array is initialized by line_init, which is an initcall. The
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* individual elements are protected by individual semaphores.
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*/
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struct line vts[MAX_TTYS] = { LINE_INIT(CONFIG_CON_ZERO_CHAN, &driver),
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[ 1 ... MAX_TTYS - 1 ] =
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LINE_INIT(CONFIG_CON_CHAN, &driver) };
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static struct line vts[MAX_TTYS] = { LINE_INIT(CONFIG_CON_ZERO_CHAN, &driver),
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[ 1 ... MAX_TTYS - 1 ] =
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LINE_INIT(CONFIG_CON_CHAN, &driver) };
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static int con_config(char *str)
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{
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@ -11,6 +11,7 @@
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#include "linux/tty.h"
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#include "linux/interrupt.h"
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#include "linux/spinlock.h"
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#include "linux/mutex.h"
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#include "chan_user.h"
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#include "mconsole_kern.h"
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@ -32,15 +33,17 @@ struct line_driver {
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struct line {
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struct tty_struct *tty;
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spinlock_t count_lock;
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int valid;
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struct mutex open_mutex;
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char *init_str;
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int init_pri;
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struct list_head chan_list;
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int valid;
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int count;
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int throttled;
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/*This lock is actually, mostly, local to*/
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spinlock_t lock;
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int throttled;
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/* Yes, this is a real circular buffer.
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* XXX: And this should become a struct kfifo!
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*
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};
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#define LINE_INIT(str, d) \
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{ .init_str = str, \
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{ .count_lock = SPIN_LOCK_UNLOCKED, \
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.init_str = str, \
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.init_pri = INIT_STATIC, \
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.valid = 1, \
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.lock = SPIN_LOCK_UNLOCKED, \
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