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SubjectRe: [PATCH] tty race on con_close and con_flush_chars

Hello,

At 29 Oct 2001 22:13:55 -0500,
Robert Love wrote:
>
> Someone pointed out (via private email) that a race can still exist
> between checking that vt is non-zero and acquiring the semaphore,
> especially since we can sleep doing that.
>
> I agree; the following patch should alleviate that race.

Your patch only fixes con_flush_chars(), but the same races exists in
do_con_write() and maybe con_unthrottle(). I think the patch below is
better because the oops would never happen with this patch.


diff -r -u -N linux.org/drivers/char/console.c linux/drivers/char/console.c
--- linux.org/drivers/char/console.c Tue Oct 30 18:55:17 2001
+++ linux/drivers/char/console.c Tue Oct 30 19:07:08 2001
@@ -2424,7 +2424,6 @@
return;
if (tty->count != 1) return;
vcs_make_devfs (MINOR (tty->device) - tty->driver.minor_start, 1);
- tty->driver_data = 0;
}

static void vc_init(unsigned int currcons, unsigned int rows, unsigned int cols, int do_clear)


>
> diff -u linux-2.4.13-ac5/drivers/char/console.c
> linux/drivers/char/console.c
> --- linux-2.4.13-ac5/drivers/char/console.c Mon Oct 29 17:27:19 2001
> +++ linux/drivers/char/console.c Mon Oct 29 22:11:27 2001
> @@ -2387,8 +2387,14 @@
> return;
>
> pm_access(pm_con);
> +
> + /*
> + * If we raced with con_close(), `vt' may be null.
> + * Hence this bandaid. - akpm
> + */
> acquire_console_sem();
> - set_cursor(vt->vc_num);
> + if (vt)
> + set_cursor(vt->vc_num);
> release_console_sem();
> }
>
>
> Robert Love
>
-
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