[PATCH] uml: redo console locking

Fix some console locking problems (including scheduling in atomic) and various
reorderings and cleanup in that code.  Not yet ready for 2.6.12 probably.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 202 insertions, 116 deletions

diff --git a/arch/um/drivers/line.c b/arch/um/drivers/line.c
index 6924f273ced9..d0f97127adf6 100644
--- a/arch/um/drivers/line.c
+++ b/arch/um/drivers/line.c
@@ -39,19 +39,69 @@ static void line_timer_cb(void *arg)
         line_interrupt(line->driver->read_irq, arg, NULL);
 }
 
-static int write_room(struct line *dev)
+/* Returns the free space inside the ring buffer of this line.
+ *
+ * Should be called while holding line->lock (this does not modify datas).
+ */
+static int write_room(struct line *line)
 {
         int n;
 
-        if (dev->buffer == NULL)
-                return (LINE_BUFSIZE - 1);
+        if (line->buffer == NULL)
+                return LINE_BUFSIZE - 1;
+
+        /* This is for the case where the buffer is wrapped! */
+        n = line->head - line->tail;
 
-        n = dev->head - dev->tail;
         if (n <= 0)
-                n = LINE_BUFSIZE + n;
-        return (n - 1);
+                n = LINE_BUFSIZE + n; /* The other case */
+        return n - 1;
+}
+
+int line_write_room(struct tty_struct *tty)
+{
+        struct line *line = tty->driver_data;
+        unsigned long flags;
+        int room;
+
+        if (tty->stopped)
+                return 0;
+
+        spin_lock_irqsave(&line->lock, flags);
+        room = write_room(line);
+        spin_unlock_irqrestore(&line->lock, flags);
+
+        /*XXX: Warning to remove */
+        if (0 == room)
+                printk(KERN_DEBUG "%s: %s: no room left in buffer\n",
+                       __FUNCTION__,tty->name);
+        return room;
 }
 
+int line_chars_in_buffer(struct tty_struct *tty)
+{
+        struct line *line = tty->driver_data;
+        unsigned long flags;
+        int ret;
+
+        spin_lock_irqsave(&line->lock, flags);
+
+        /*write_room subtracts 1 for the needed NULL, so we readd it.*/
+        ret = LINE_BUFSIZE - (write_room(line) + 1);
+        spin_unlock_irqrestore(&line->lock, flags);
+
+        return ret;
+}
+
+/*
+ * This copies the content of buf into the circular buffer associated with
+ * this line.
+ * The return value is the number of characters actually copied, i.e. the ones
+ * for which there was space: this function is not supposed to ever flush out
+ * the circular buffer.
+ *
+ * Must be called while holding line->lock!
+ */
 static int buffer_data(struct line *line, const char *buf, int len)
 {
         int end, room;
@@ -70,48 +120,95 @@ static int buffer_data(struct line *line, const char *buf, int len)
         len = (len > room) ? room : len;
 
         end = line->buffer + LINE_BUFSIZE - line->tail;
-        if(len < end){
+
+        if (len < end){
                 memcpy(line->tail, buf, len);
                 line->tail += len;
-        }
-        else {
+        } else {
+                /* The circular buffer is wrapping */
                 memcpy(line->tail, buf, end);
                 buf += end;
                 memcpy(line->buffer, buf, len - end);
                 line->tail = line->buffer + len - end;
         }
 
-        return(len);
+        return len;
 }
 
+/*
+ * Flushes the ring buffer to the output channels. That is, write_chan is
+ * called, passing it line->head as buffer, and an appropriate count.
+ *
+ * On exit, returns 1 when the buffer is empty,
+ * 0 when the buffer is not empty on exit,
+ * and -errno when an error occurred.
+ *
+ * Must be called while holding line->lock!*/
 static int flush_buffer(struct line *line)
 {
         int n, count;
 
         if ((line->buffer == NULL) || (line->head == line->tail))
-                return(1);
+                return 1;
 
         if (line->tail < line->head) {
+                /* line->buffer + LINE_BUFSIZE is the end of the buffer! */
                 count = line->buffer + LINE_BUFSIZE - line->head;
+
                 n = write_chan(&line->chan_list, line->head, count,
                                line->driver->write_irq);
                 if (n < 0)
-                        return(n);
-                if (n == count)
+                        return n;
+                if (n == count) {
+                        /* We have flushed from ->head to buffer end, now we
+                         * must flush only from the beginning to ->tail.*/
                         line->head = line->buffer;
-                else {
+                } else {
                         line->head += n;
-                        return(0);
+                        return 0;
                 }
         }
 
         count = line->tail - line->head;
         n = write_chan(&line->chan_list, line->head, count, 
                        line->driver->write_irq);
-        if(n < 0) return(n);
+
+        if(n < 0)
+                return n;
 
         line->head += n;
-        return(line->head == line->tail);
+        return line->head == line->tail;
+}
+
+void line_flush_buffer(struct tty_struct *tty)
+{
+        struct line *line = tty->driver_data;
+        unsigned long flags;
+        int err;
+
+        /*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);
+        /*if (err == 1)
+                err = 0;*/
+        spin_unlock_irqrestore(&line->lock, flags);
+        //return err;
+}
+
+/* We map both ->flush_chars and ->put_char (which go in pair) onto ->flush_buffer
+ * and ->write. Hope it's not that bad.*/
+void line_flush_chars(struct tty_struct *tty)
+{
+        line_flush_buffer(tty);
+}
+
+void line_put_char(struct tty_struct *tty, unsigned char ch)
+{
+        line_write(tty, &ch, sizeof(ch));
 }
 
 int line_write(struct tty_struct *tty, const unsigned char *buf, int len)
@@ -120,38 +217,31 @@ int line_write(struct tty_struct *tty, const unsigned char *buf, int len)
         unsigned long flags;
         int n, err, ret = 0;
 
-        if(tty->stopped) return 0;
+        if(tty->stopped)
+                return 0;
 
-        down(&line->sem);
-        if(line->head != line->tail){
-                local_irq_save(flags);
+        spin_lock_irqsave(&line->lock, flags);
+        if (line->head != line->tail) {
                 ret = buffer_data(line, buf, len);
                 err = flush_buffer(line);
-                local_irq_restore(flags);
-                if(err <= 0 && (err != -EAGAIN || !ret))
+                if (err <= 0 && (err != -EAGAIN || !ret))
                         ret = err;
-        }
-        else {
+        } else {
                 n = write_chan(&line->chan_list, buf, len, 
                                line->driver->write_irq);
-                if(n < 0){
+                if (n < 0) {
                         ret = n;
                         goto out_up;
                 }
 
                 len -= n;
                 ret += n;
-                if(len > 0)
+                if (len > 0)
                         ret += buffer_data(line, buf + n, len);
         }
- out_up:
-        up(&line->sem);
-        return(ret);
-}
-
-void line_put_char(struct tty_struct *tty, unsigned char ch)
-{
-        line_write(tty, &ch, sizeof(ch));
+out_up:
+        spin_unlock_irqrestore(&line->lock, flags);
+        return ret;
 }
 
 void line_set_termios(struct tty_struct *tty, struct termios * old)
@@ -159,11 +249,6 @@ void line_set_termios(struct tty_struct *tty, struct termios * old)
         /* nothing */
 }
 
-int line_chars_in_buffer(struct tty_struct *tty)
-{
-        return 0;
-}
-
 static struct {
         int  cmd;
         char *level;
@@ -250,7 +335,7 @@ int line_ioctl(struct tty_struct *tty, struct file * file,
                 ret = -ENOIOCTLCMD;
                 break;
         }
-        return(ret);
+        return ret;
 }
 
 static irqreturn_t line_write_interrupt(int irq, void *data,
@@ -260,18 +345,23 @@ static irqreturn_t line_write_interrupt(int irq, void *data,
         struct line *line = tty->driver_data;
         int err;
 
+        /* Interrupts are enabled here because we registered the interrupt with
+         * SA_INTERRUPT (see line_setup_irq).*/
+
+        spin_lock_irq(&line->lock);
         err = flush_buffer(line);
-        if(err == 0)
-                return(IRQ_NONE);
-        else if(err < 0){
+        if (err == 0) {
+                return IRQ_NONE;
+        } else if(err < 0) {
                 line->head = line->buffer;
                 line->tail = line->buffer;
         }
+        spin_unlock_irq(&line->lock);
 
         if(tty == NULL)
-                return(IRQ_NONE);
+                return IRQ_NONE;
 
-        if(test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags) &&
+        if (test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags) &&
            (tty->ldisc.write_wakeup != NULL))
                 (tty->ldisc.write_wakeup)(tty);
         
@@ -281,9 +371,9 @@ static irqreturn_t line_write_interrupt(int irq, void *data,
          * writes.
          */
 
-        if(waitqueue_active(&tty->write_wait))
+        if (waitqueue_active(&tty->write_wait))
                 wake_up_interruptible(&tty->write_wait);
-        return(IRQ_HANDLED);
+        return IRQ_HANDLED;
 }
 
 int line_setup_irq(int fd, int input, int output, struct tty_struct *tty)
@@ -292,15 +382,18 @@ int line_setup_irq(int fd, int input, int output, struct tty_struct *tty)
         struct line_driver *driver = line->driver;
         int err = 0, flags = SA_INTERRUPT | SA_SHIRQ | SA_SAMPLE_RANDOM;
 
-        if(input) err = um_request_irq(driver->read_irq, fd, IRQ_READ, 
+        if (input)
+                err = um_request_irq(driver->read_irq, fd, IRQ_READ,
                                        line_interrupt, flags, 
                                        driver->read_irq_name, tty);
-        if(err) return(err);
-        if(output) err = um_request_irq(driver->write_irq, fd, IRQ_WRITE, 
+        if (err)
+                return err;
+        if (output)
+                err = um_request_irq(driver->write_irq, fd, IRQ_WRITE,
                                         line_write_interrupt, flags, 
                                         driver->write_irq_name, tty);
         line->have_irq = 1;
-        return(err);
+        return err;
 }
 
 void line_disable(struct tty_struct *tty, int current_irq)
@@ -336,7 +429,9 @@ int line_open(struct line *lines, struct tty_struct *tty,
         line = &lines[tty->index];
         tty->driver_data = line;
 
-        down(&line->sem);
+        /* 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);
         if (tty->count == 1) {
                 if (!line->valid) {
                         err = -ENODEV;
@@ -349,6 +444,7 @@ int line_open(struct line *lines, struct tty_struct *tty,
                         err = open_chan(&line->chan_list);
                         if(err) goto out;
                 }
+                /* Here the interrupt is registered.*/
                 enable_chan(&line->chan_list, tty);
                 INIT_WORK(&line->task, line_timer_cb, tty);
         }
@@ -362,21 +458,27 @@ int line_open(struct line *lines, struct tty_struct *tty,
         line->count++;
 
 out:
-        up(&line->sem);
-        return(err);
+        spin_unlock(&line->lock);
+        return err;
 }
 
 void line_close(struct tty_struct *tty, struct file * filp)
 {
         struct line *line = tty->driver_data;
 
-        down(&line->sem);
+        /* XXX: I assume this should be called in process context, not with interrupt
+         * disabled!*/
+        spin_lock_irq(&line->lock);
+
+        /* We ignore the error anyway! */
+        flush_buffer(line);
+
         line->count--;
         if (tty->count == 1) {
                 line_disable(tty, -1);
                 tty->driver_data = NULL;
         }
-        up(&line->sem);
+        spin_unlock_irq(&line->lock);
 }
 
 void close_lines(struct line *lines, int nlines)
@@ -387,31 +489,41 @@ void close_lines(struct line *lines, int nlines)
                 close_chan(&lines[i].chan_list);
 }
 
-int line_setup(struct line *lines, int num, char *init, int all_allowed)
+/* Common setup code for both startup command line and mconsole initialization.
+ * @lines contains the the array (of size @num) to modify;
+ * @init is the setup string;
+ * @all_allowed is a boolean saying if we can setup the whole @lines
+ * at once. For instance, it will be usually true for startup init. (where we
+ * can use con=xterm) and false for mconsole.*/
+
+int line_setup(struct line *lines, unsigned int num, char *init, int all_allowed)
 {
         int i, n;
         char *end;
 
-        if(*init == '=') n = -1;
-        else {
+        if(*init == '=') {
+                /* We said con=/ssl= instead of con#=, so we are configuring all
+                 * consoles at once.*/
+                n = -1;
+        } else {
                 n = simple_strtoul(init, &end, 0);
                 if(*end != '='){
                         printk(KERN_ERR "line_setup failed to parse \"%s\"\n", 
                                init);
-                        return(0);
+                        return 0;
                 }
                 init = end;
         }
         init++;
-        if((n >= 0) && (n >= num)){
+
+        if (n >= (signed int) num) {
                 printk("line_setup - %d out of range ((0 ... %d) allowed)\n",
                        n, num - 1);
-                return(0);
-        }
-        else if (n >= 0){
+                return 0;
+        } else if (n >= 0){
                 if (lines[n].count > 0) {
                         printk("line_setup - device %d is open\n", n);
-                        return(0);
+                        return 0;
                 }
                 if (lines[n].init_pri <= INIT_ONE){
                         lines[n].init_pri = INIT_ONE;
@@ -422,13 +534,11 @@ int line_setup(struct line *lines, int num, char *init, int all_allowed)
                                 lines[n].valid = 1;
                         }       
                 }
-        }
-        else if(!all_allowed){
+        } else if(!all_allowed){
                 printk("line_setup - can't configure all devices from "
                        "mconsole\n");
-                return(0);
-        }
-        else {
+                return 0;
+        } else {
                 for(i = 0; i < num; i++){
                         if(lines[i].init_pri <= INIT_ALL){
                                 lines[i].init_pri = INIT_ALL;
@@ -440,21 +550,21 @@ int line_setup(struct line *lines, int num, char *init, int all_allowed)
                         }
                 }
         }
-        return(1);
+        return 1;
 }
 
-int line_config(struct line *lines, int num, char *str)
+int line_config(struct line *lines, unsigned int num, char *str)
 {
         char *new = uml_strdup(str);
 
         if(new == NULL){
                 printk("line_config - uml_strdup failed\n");
-                return(-ENOMEM);
+                return -ENOMEM;
         }
-        return(!line_setup(lines, num, new, 0));
+        return !line_setup(lines, num, new, 0);
 }
 
-int line_get_config(char *name, struct line *lines, int num, char *str, 
+int line_get_config(char *name, struct line *lines, unsigned int num, char *str,
                     int size, char **error_out)
 {
         struct line *line;
@@ -464,47 +574,33 @@ int line_get_config(char *name, struct line *lines, int num, char *str,
         dev = simple_strtoul(name, &end, 0);
         if((*end != '\0') || (end == name)){
                 *error_out = "line_get_config failed to parse device number";
-                return(0);
+                return 0;
         }
 
         if((dev < 0) || (dev >= num)){
-                *error_out = "device number of of range";
-                return(0);
+                *error_out = "device number out of range";
+                return 0;
         }
 
         line = &lines[dev];
 
-        down(&line->sem);
+        spin_lock(&line->lock);
         if(!line->valid)
                 CONFIG_CHUNK(str, size, n, "none", 1);
         else if(line->count == 0)
                 CONFIG_CHUNK(str, size, n, line->init_str, 1);
         else n = chan_config_string(&line->chan_list, str, size, error_out);
-        up(&line->sem);
+        spin_unlock(&line->lock);
 
-        return(n);
+        return n;
 }
 
-int line_remove(struct line *lines, int num, char *str)
+int line_remove(struct line *lines, unsigned int num, char *str)
 {
         char config[sizeof("conxxxx=none\0")];
 
         sprintf(config, "%s=none", str);
-        return(!line_setup(lines, num, config, 0));
-}
-
-int line_write_room(struct tty_struct *tty)
-{
-        struct line *dev = tty->driver_data;
-        int room;
-
-        if (tty->stopped)
-                return 0;
-        room = write_room(dev);
-        if (0 == room)
-                printk(KERN_DEBUG "%s: %s: no room left in buffer\n",
-                       __FUNCTION__,tty->name);
-        return room;
+        return !line_setup(lines, num, config, 0);
 }
 
 struct tty_driver *line_register_devfs(struct lines *set,
@@ -553,7 +649,7 @@ void lines_init(struct line *lines, int nlines)
         for(i = 0; i < nlines; i++){
                 line = &lines[i];
                 INIT_LIST_HEAD(&line->chan_list);
-                sema_init(&line->sem, 1);
+                spin_lock_init(&line->lock);
                 if(line->init_str != NULL){
                         line->init_str = uml_strdup(line->init_str);
                         if(line->init_str == NULL)
@@ -587,7 +683,7 @@ irqreturn_t winch_interrupt(int irq, void *data, struct pt_regs *unused)
                                        "errno = %d\n", -err);
                                 printk("fd %d is losing SIGWINCH support\n",
                                        winch->tty_fd);
-                                return(IRQ_HANDLED);
+                                return IRQ_HANDLED;
                         }
                         goto out;
                 }
@@ -603,7 +699,7 @@ irqreturn_t winch_interrupt(int irq, void *data, struct pt_regs *unused)
  out:
         if(winch->fd != -1)
                 reactivate_fd(winch->fd, WINCH_IRQ);
-        return(IRQ_HANDLED);
+        return IRQ_HANDLED;
 }
 
 DECLARE_MUTEX(winch_handler_sem);
@@ -625,7 +721,7 @@ void register_winch_irq(int fd, int tty_fd, int pid, struct tty_struct *tty)
                                    .pid         = pid,
                                    .tty         = tty });
         list_add(&winch->list, &winch_handlers);
-        if(um_request_irq(WINCH_IRQ, fd, IRQ_READ, winch_interrupt, 
+        if(um_request_irq(WINCH_IRQ, fd, IRQ_READ, winch_interrupt,
                           SA_INTERRUPT | SA_SHIRQ | SA_SAMPLE_RANDOM, 
                           "winch", winch) < 0)
                 printk("register_winch_irq - failed to register IRQ\n");
@@ -656,26 +752,16 @@ char *add_xterm_umid(char *base)
         int len;
 
         umid = get_umid(1);
-        if(umid == NULL) return(base);
+        if(umid == NULL)
+                return base;
         
         len = strlen(base) + strlen(" ()") + strlen(umid) + 1;
         title = kmalloc(len, GFP_KERNEL);
         if(title == NULL){
                 printk("Failed to allocate buffer for xterm title\n");
-                return(base);
+                return base;
         }
 
         snprintf(title, len, "%s (%s)", base, umid);
-        return(title);
+        return title;
 }
-
-/*
- * Overrides for Emacs so that we follow Linus's tabbing style.
- * Emacs will notice this stuff at the end of the file and automatically
- * adjust the settings for this buffer only.  This must remain at the end
- * of the file.
- * ---------------------------------------------------------------------------
- * Local variables:
- * c-file-style: "linux"
- * End:
- */