diff options
Diffstat (limited to 'arch/um')
| -rw-r--r-- | arch/um/drivers/line.c | 48 | ||||
| -rw-r--r-- | arch/um/include/line.h | 1 |
2 files changed, 8 insertions, 41 deletions
diff --git a/arch/um/drivers/line.c b/arch/um/drivers/line.c index 433e572fb19..0e1e9a20a4d 100644 --- a/arch/um/drivers/line.c +++ b/arch/um/drivers/line.c @@ -425,42 +425,15 @@ int line_setup_irq(int fd, int input, int output, struct line *line, void *data) * 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. + * mconsole config requests will want to be sure the device isn't in + * use, and get_config, open, and close will want a stable + * configuration. The checking and modification of the configuration + * is done under a spinlock. Checking whether the device is in use is + * line->tty->count > 1, also under the spinlock. * - * 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. + * tty->count serves to decide whether the device should be enabled or + * disabled on the host. If it's equal to 1, then we are doing the + * first open or last close. Otherwise, open and close just return. */ int line_open(struct line *lines, struct tty_struct *tty) @@ -476,7 +449,6 @@ int line_open(struct line *lines, struct tty_struct *tty) if(tty->count > 1) goto out_unlock; - mutex_lock(&line->open_mutex); spin_unlock(&line->count_lock); tty->driver_data = line; @@ -493,7 +465,6 @@ int line_open(struct line *lines, struct tty_struct *tty) chan_window_size(&line->chan_list, &tty->winsize.ws_row, &tty->winsize.ws_col); - mutex_unlock(&line->open_mutex); return err; out_unlock: @@ -523,7 +494,6 @@ void line_close(struct tty_struct *tty, struct file * filp) if(tty->count > 1) goto out_unlock; - mutex_lock(&line->open_mutex); spin_unlock(&line->count_lock); line->tty = NULL; @@ -534,7 +504,6 @@ void line_close(struct tty_struct *tty, struct file * filp) line->sigio = 0; } - mutex_unlock(&line->open_mutex); return; out_unlock: @@ -755,7 +724,6 @@ void lines_init(struct line *lines, int nlines, struct chan_opts *opts) 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; diff --git a/arch/um/include/line.h b/arch/um/include/line.h index 3477a858eaa..1223f2c844b 100644 --- a/arch/um/include/line.h +++ b/arch/um/include/line.h @@ -35,7 +35,6 @@ struct line { spinlock_t count_lock; int valid; - struct mutex open_mutex; char *init_str; int init_pri; struct list_head chan_list; |