Messages in this thread | | | Date | Mon, 4 Dec 2006 00:29:26 +0300 | From | Oleg Nesterov <> | Subject | Re: [PATCH] introduce put_pid_rcu() to fix unsafe put_pid(vc->vt_pid) |
| |
On 12/03, Andrew Morton wrote: > > On Sat, 2 Dec 2006 02:48:26 +0300 > Oleg Nesterov <oleg@tv-sign.ru> wrote: > > > drivers/char/vt_ioctl.c changes vc->vt_pid doing > > > > put_pid(xchg(&vc->vt_pid, ...)); > > > > This is unsafe, put_pid() can actually free the memory while vc->vt_pid is > > still used by kill_pid(vc->vt_pid). > > > > Add a new helper, put_pid_rcu(), which frees "struct pid" via rcu callback > > and convert vt_ioctl.c to use it. > > > > > I'm a bit reluctant to go adding more tricky infrastructure (especially > 100% undocumented infrastructure) on behalf of a single usage site in a > place as creepy as the VT ioctl code. > If we envisage future users of this infrastructure (and if it gets > documented) then OK.
It is a shame we can't use "struct pid*" lockless, note that "struct pid" itself is rcu-protected. I hope we can find another usage for put_pid_rcu (in fact I suggested it before, but didn't have a reason). However, I don't see any other example immediately.
> Otherwise I'd rather just stick another bandaid into > the vt code. Can we add some locking there,
Yes, this is possible, and probably we should do just this.
> or change it to use a > task_struct* or something?
I don't think this is good. It was converted from task_struct* to pid*.
Eric, what do you think?
Oleg.
- 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/
| |