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

>
> On Mon, 3 Mar 2003, Nicolas Pitre wrote:
> >
> > 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.
>
> Looks ok. I would suggest moving the "spin_lock_irqsave()" to outside the
> 'if'-statement, though, since that should make the code a lot more
> readable, and if the lock is supposed to protect tty->flip.buf_num, then
> let's do it right and protect the read as well, no?

Oh sure.

--- 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 16:49:44 2003
@@ -1944,27 +1944,25 @@
schedule_delayed_work(&tty->flip.work, 1);
return;
}
+
+ spin_lock_irqsave(&tty->read_lock, flags);
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?
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?
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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