Commit fb5c594c authored by Michal Ostrowski's avatar Michal Ostrowski Committed by Paul Mackerras

[PATCH] Fix race condition in hvc console.

tty_schedule_flip() would schedule a thread that would call flush_to_ldisc().
If tty_buffer_request_room() gets called prior to that thread running --
which is likely in this loop in hvc_poll(), it would set the active flag
in the tty buffer and consequently flush_to_ldisc() would ignore it.

The result is that input on the hvc console is not processed.

This fix calls tty_flip_buffer_push (and flags the tty as
"low_latency").  The push to the ldisc thus happens synchronously.
Signed-off-by: default avatarMichal Ostrowski <mostrows@watson.ibm.com>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 4558f417
...@@ -335,6 +335,8 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) ...@@ -335,6 +335,8 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
} /* else count == 0 */ } /* else count == 0 */
tty->driver_data = hp; tty->driver_data = hp;
tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */
hp->tty = tty; hp->tty = tty;
/* Save for request_irq outside of spin_lock. */ /* Save for request_irq outside of spin_lock. */
irq = hp->irq; irq = hp->irq;
...@@ -633,9 +635,6 @@ static int hvc_poll(struct hvc_struct *hp) ...@@ -633,9 +635,6 @@ static int hvc_poll(struct hvc_struct *hp)
tty_insert_flip_char(tty, buf[i], 0); tty_insert_flip_char(tty, buf[i], 0);
} }
if (count)
tty_schedule_flip(tty);
/* /*
* Account for the total amount read in one loop, and if above * Account for the total amount read in one loop, and if above
* 64 bytes, we do a quick schedule loop to let the tty grok * 64 bytes, we do a quick schedule loop to let the tty grok
...@@ -656,6 +655,9 @@ static int hvc_poll(struct hvc_struct *hp) ...@@ -656,6 +655,9 @@ static int hvc_poll(struct hvc_struct *hp)
bail: bail:
spin_unlock_irqrestore(&hp->lock, flags); spin_unlock_irqrestore(&hp->lock, flags);
if (read_total)
tty_flip_buffer_push(tty);
return poll_mask; return poll_mask;
} }
......
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