tty: hvc: hvc_poll() break hv read loop

Avoid looping with the spinlock held while there is read data
being returned from the hv driver. Instead note if the entire
size returned by tty_buffer_request_room was read, and request
another read poll.

This limits the critical section lengths, and provides more
even service to other consoles in case there is a pathological
condition.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index fddb63322c6786333920cc5c9837d2da5c9cb9bf..745ac220fce84c23ea811d83952a2771eda7cf30 100644 (file)
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -592,7 +592,7 @@ static u32 timeout = MIN_TIMEOUT;
 int hvc_poll(struct hvc_struct *hp)
 {
        struct tty_struct *tty;
-       int i, n, poll_mask = 0;
+       int i, n, count, poll_mask = 0;
        char buf[N_INBUF] __ALIGNED__;
        unsigned long flags;
        int read_total = 0;
@@ -618,7 +618,7 @@ int hvc_poll(struct hvc_struct *hp)
 
        /* Now check if we can get data (are we throttled ?) */
        if (tty_throttled(tty))
-               goto throttled;
+               goto out;
 
        /* If we aren't notifier driven and aren't throttled, we always
         * request a reschedule
@@ -627,56 +627,58 @@ int hvc_poll(struct hvc_struct *hp)
                poll_mask |= HVC_POLL_READ;
 
        /* Read data if any */
-       for (;;) {
-               int count = tty_buffer_request_room(&hp->port, N_INBUF);
 
-               /* If flip is full, just reschedule a later read */
-               if (count == 0) {
+       count = tty_buffer_request_room(&hp->port, N_INBUF);
+
+       /* If flip is full, just reschedule a later read */
+       if (count == 0) {
+               poll_mask |= HVC_POLL_READ;
+               goto out;
+       }
+
+       n = hp->ops->get_chars(hp->vtermno, buf, count);
+       if (n <= 0) {
+               /* Hangup the tty when disconnected from host */
+               if (n == -EPIPE) {
+                       spin_unlock_irqrestore(&hp->lock, flags);
+                       tty_hangup(tty);
+                       spin_lock_irqsave(&hp->lock, flags);
+               } else if ( n == -EAGAIN ) {
+                       /*
+                        * Some back-ends can only ensure a certain min
+                        * num of bytes read, which may be > 'count'.
+                        * Let the tty clear the flip buff to make room.
+                        */
                        poll_mask |= HVC_POLL_READ;
-                       break;
                }
+               goto out;
+       }
 
-               n = hp->ops->get_chars(hp->vtermno, buf, count);
-               if (n <= 0) {
-                       /* Hangup the tty when disconnected from host */
-                       if (n == -EPIPE) {
-                               spin_unlock_irqrestore(&hp->lock, flags);
-                               tty_hangup(tty);
-                               spin_lock_irqsave(&hp->lock, flags);
-                       } else if ( n == -EAGAIN ) {
-                               /*
-                                * Some back-ends can only ensure a certain min
-                                * num of bytes read, which may be > 'count'.
-                                * Let the tty clear the flip buff to make room.
-                                */
-                               poll_mask |= HVC_POLL_READ;
-                       }
-                       break;
-               }
-               for (i = 0; i < n; ++i) {
+       for (i = 0; i < n; ++i) {
 #ifdef CONFIG_MAGIC_SYSRQ
-                       if (hp->index == hvc_console.index) {
-                               /* Handle the SysRq Hack */
-                               /* XXX should support a sequence */
-                               if (buf[i] == '\x0f') { /* ^O */
-                                       /* if ^O is pressed again, reset
-                                        * sysrq_pressed and flip ^O char */
-                                       sysrq_pressed = !sysrq_pressed;
-                                       if (sysrq_pressed)
-                                               continue;
-                               } else if (sysrq_pressed) {
-                                       handle_sysrq(buf[i]);
-                                       sysrq_pressed = 0;
+               if (hp->index == hvc_console.index) {
+                       /* Handle the SysRq Hack */
+                       /* XXX should support a sequence */
+                       if (buf[i] == '\x0f') { /* ^O */
+                               /* if ^O is pressed again, reset
+                                * sysrq_pressed and flip ^O char */
+                               sysrq_pressed = !sysrq_pressed;
+                               if (sysrq_pressed)
                                        continue;
-                               }
+                       } else if (sysrq_pressed) {
+                               handle_sysrq(buf[i]);
+                               sysrq_pressed = 0;
+                               continue;
                        }
-#endif /* CONFIG_MAGIC_SYSRQ */
-                       tty_insert_flip_char(&hp->port, buf[i], 0);
                }
-
-               read_total += n;
+#endif /* CONFIG_MAGIC_SYSRQ */
+               tty_insert_flip_char(&hp->port, buf[i], 0);
        }
- throttled:
+       if (n == count)
+               poll_mask |= HVC_POLL_READ;
+       read_total = n;
+
+ out:
        /* Wakeup write queue if necessary */
        if (hp->do_wakeup) {
                hp->do_wakeup = 0;