On Wed, Nov 12, 2014 at 02:33:00PM +1030, Rusty Russell wrote: > Amos Kong <akong@xxxxxxxxxx> writes: > > From: Rusty Russell <rusty@xxxxxxxxxxxxxxx> > > > > The previous patch added one potential problem: we can still be > > reading from a hwrng when it's unregistered. Add a wait for zero > > in the hwrng_unregister path. > > > > v4: add cleanup_done flag to insure that cleanup is done > > That's a bit weird. The usual pattern would be to hold a reference > until we're actually finished, but this reference is a bit weird. > > We hold the mutex across cleanup, so we could grab that but we have to > take care sleeping inside wait_event, otherwise Peter will have to fix > my code again :) > > AFAICT the wake_woken() stuff isn't merged yet, so your patch will > have to do for now. > > > @@ -98,6 +99,8 @@ static inline void cleanup_rng(struct kref *kref) > > > > if (rng->cleanup) > > rng->cleanup(rng); > > + rng->cleanup_done = true; > > + wake_up_all(&rng_done); > > } > > > > static void set_current_rng(struct hwrng *rng) > > @@ -536,6 +539,11 @@ void hwrng_unregister(struct hwrng *rng) > > kthread_stop(hwrng_fill); > > } else > > mutex_unlock(&rng_mutex); > > + > > + /* Just in case rng is reading right now, wait. */ > > + wait_event(rng_done, rng->cleanup_done && > > + atomic_read(&rng->ref.refcount) == 0); > > + > > The atomic_read() isn't necessary here. At least, we need it to convert refcount from atomic_t to int. Otherwise, we will touch this error: error: invalid operands to binary == (have 'atomic_t' and 'int') > However, you should probably init cleanup_done in hwrng_register(). > (Probably noone does unregister then register, but let's be clear). > > Thanks, > Rusty. -- Amos.
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