Messages in this thread | | | Date | Tue, 31 Jan 2012 10:59:55 -0500 | From | Ted Ts'o <> | Subject | Re: [PATCH] char random: fix boot id uniqueness race |
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On Sun, Jan 29, 2012 at 11:40:12PM -0500, Mathieu Desnoyers wrote: > Index: linux-2.6-lttng/drivers/char/random.c > =================================================================== > --- linux-2.6-lttng.orig/drivers/char/random.c > +++ linux-2.6-lttng/drivers/char/random.c > @@ -1231,6 +1231,8 @@ static int min_read_thresh = 8, min_writ > static int max_read_thresh = INPUT_POOL_WORDS * 32; > static int max_write_thresh = INPUT_POOL_WORDS * 32; > static char sysctl_bootid[16]; > +static int boot_id_generated; > +static DEFINE_MUTEX(boot_id_mutex);
My preference would be to put these statics in proc_do_uuid(), but that's arguably a nit.
> + } else { > + if (unlikely(!ACCESS_ONCE(boot_id_generated))) { > + mutex_lock(&boot_id_mutex); > + if (!boot_id_generated) { > + generate_random_uuid(uuid); > + /* Store uuid before boot_id_generated. */ > + smp_wmb(); > + boot_id_generated = 1; > + } > + mutex_unlock(&boot_id_mutex); > + } else { > + /* Load boot_id_generated before uuid */ > + smp_rmb(); > + } > + }
I don't believe the smp_wmb() and smp_rmb() are necessary here; the mutex_lock() and mutex_unlock() should put the necessary memory barriers in place.
Regards,
- Ted
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