Messages in this thread Patch in this message |  | | | Date | Mon, 10 Dec 2001 22:28:42 -0800 | | From | Andrew Morton <> | | Subject | Re: [PATCH] console close race fix resend |
Robert Love wrote: > > On Mon, 2001-12-10 at 22:16, Gordon Oliver wrote: > > > and (c) appears to still have a race... You should extract > > the value from the structure inside the lock, otherwise you > > will still race with con_close (though perhaps a smaller race) > > but since the call to acquire_console_sem() can sleep, the > > vt handle you have may be stale. > > Ehh, I don't think so. Here is the whole patched function: > > static void con_flush_chars(struct tty_struct *tty) > { > struct vt_struct *vt = (struct vt_struct *)tty->driver_data; > if (in_interrupt()) /* from flush_to_ldisc */ > return; > pm_access(pm_con); > acquire_console_sem(); > if (vt) > set_cursor(vt->vc_num); > release_console_sem(); > } >
It could be improved - we really should test tty->driver_data inside lock_kernel(), and after the possible sleep.
How does this look (and how does it test?)
--- linux-2.4.17-pre8/drivers/char/console.c Mon Dec 10 13:46:20 2001 +++ linux-akpm/drivers/char/console.c Mon Dec 10 22:27:05 2001 @@ -100,6 +100,7 @@ #include <linux/tqueue.h> #include <linux/bootmem.h> #include <linux/pm.h> +#include <linux/smp_lock.h> #include <asm/io.h> #include <asm/system.h> @@ -2350,15 +2351,18 @@ static void con_start(struct tty_struct static void con_flush_chars(struct tty_struct *tty) { - struct vt_struct *vt = (struct vt_struct *)tty->driver_data; + struct vt_struct *vt; if (in_interrupt()) /* from flush_to_ldisc */ return; - pm_access(pm_con); + lock_kernel(); /* versus con_close() */ acquire_console_sem(); - set_cursor(vt->vc_num); + vt = (struct vt_struct *)tty->driver_data; + if (vt) + set_cursor(vt->vc_num); release_console_sem(); + unlock_kernel(); } /* - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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