Messages in this thread |  | | | Date | Sun, 28 Aug 2005 07:56:40 +0800 | | From | "Antonino A. Daplas" <> | | Subject | Re: [PATCH] Remove race between con_open and con_close |
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Paul Mackerras wrote: > I have a laptop (G3 powerbook) which will pretty reliably hit a race > between con_open and con_close late in the boot process and oops in > vt_ioctl due to tty->driver_data being NULL. > > What happens is this: process A opens /dev/tty6; it comes into > con_open() (drivers/char/vt.c) and assign a non-NULL value to > tty->driver_data. Then process A closes that and concurrently process > B opens /dev/tty6. Process A gets through con_close() and clears > tty->driver_data, since tty->count == 1. However, before process A > can decrement tty->count, we switch to process B (e.g. at the > down(&tty_sem) call at drivers/char/tty_io.c line 1626). > > So process B gets to run and comes into con_open with tty->count == 2, > as tty->count is incremented (in init_dev) before con_open is called. > Because tty->count != 1, we don't set tty->driver_data. Then when the > process tries to do anything with that fd, it oopses. > > The simple and effective fix for this is to test tty->driver_data > rather than tty->count in con_open. The testing and setting of > tty->driver_data is serialized with respect to the clearing of > tty->driver_data in con_close by the console_sem. We can't get a > situation where con_open sees tty->driver_data != NULL and then > con_close on a different fd clears tty->driver_data, because > tty->count is incremented before con_open is called. Thus this patch > eliminates the race, and in fact with this patch my laptop doesn't > oops. > > Could this go into 2.6.13 please?
I agree this should go to 2.6.13. Though you've been beaten to the punch by Steven Rostedt. This is already in the mm tree.
http://marc.theaimsgroup.com/?l=linux-kernel&m=112450820432121&w=2
Tony
> > Signed-off-by: Paul Mackerras <paulus@samba.org> > > diff -urN linux-2.6/drivers/char/vt.c pmac-2.6/drivers/char/vt.c > --- linux-2.6/drivers/char/vt.c 2005-07-17 10:59:52.000000000 +1000 > +++ pmac-2.6/drivers/char/vt.c 2005-08-27 22:59:36.000000000 +1000 > @@ -2433,7 +2433,7 @@ > int ret = 0; > > acquire_console_sem(); > - if (tty->count == 1) { > + if (tty->driver_data == NULL) { > ret = vc_allocate(currcons); > if (ret == 0) { > struct vc_data *vc = vc_cons[currcons].d; > - > 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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