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SubjectRe: [patch] small tty irq race fix
On Mon, 3 Mar 2003, Alan Cox wrote:

>
> > fp = tty->flip.flag_buf + TTY_FLIPBUF_SIZE;
> > - tty->flip.buf_num = 0;
> >
> > local_irq_save(flags); // FIXME: is this safe?
> > + tty->flip.buf_num = 0;
>
> The other CPU can be touching these fields too surely. Its a
> useful note that the spinlocks need putting in the right spot
> but its still broken 8(

What about this one? It just happens that tty->read_lock is actually used
deeper in the same call instance (in n_tty.c) so this looks to be the best
lock to use.

--- linux-2.5.63/drivers/char/tty_io.c.orig Mon Feb 24 14:05:34 2003
+++ linux-2.5.63/drivers/char/tty_io.c Mon Mar 3 16:13:30 2003
@@ -1947,23 +1947,23 @@
if (tty->flip.buf_num) {
cp = tty->flip.char_buf + TTY_FLIPBUF_SIZE;
fp = tty->flip.flag_buf + TTY_FLIPBUF_SIZE;
- tty->flip.buf_num = 0;

- local_irq_save(flags); // FIXME: is this safe?
+ spin_lock_irqsave(&tty->read_lock, flags);
+ tty->flip.buf_num = 0;
tty->flip.char_buf_ptr = tty->flip.char_buf;
tty->flip.flag_buf_ptr = tty->flip.flag_buf;
} else {
cp = tty->flip.char_buf;
fp = tty->flip.flag_buf;
- tty->flip.buf_num = 1;

- local_irq_save(flags); // FIXME: is this safe?
+ spin_lock_irqsave(&tty->read_lock, flags);
+ tty->flip.buf_num = 1;
tty->flip.char_buf_ptr = tty->flip.char_buf + TTY_FLIPBUF_SIZE;
tty->flip.flag_buf_ptr = tty->flip.flag_buf + TTY_FLIPBUF_SIZE;
}
count = tty->flip.count;
tty->flip.count = 0;
- local_irq_restore(flags); // FIXME: is this safe?
+ spin_unlock_irqrestore(&tty->read_lock, flags);

tty->ldisc.receive_buf(tty, cp, fp, count);
}
Nicolas

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