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

drivers/char/hvc_console.c

+5 −3
Original line number Diff line number Diff line
@@ -335,6 +335,8 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) 
	} /* else count == 0 */



	tty->driver_data = hp;

	tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */



	hp->tty = tty;

	/* Save for request_irq outside of spin_lock. */

	irq = hp->irq;
@@ -633,9 +635,6 @@ static int hvc_poll(struct hvc_struct *hp) 
			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

		 * 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) 
 bail:

	spin_unlock_irqrestore(&hp->lock, flags);



	if (read_total)

		tty_flip_buffer_push(tty);

	

	return poll_mask;

}