On 2017/12/13 18:34, Christian König wrote: > Am 12.12.2017 um 22:28 schrieb David Rientjes: >> On Tue, 12 Dec 2017, Dimitri Sivanich wrote: >> >>>> --- a/drivers/misc/sgi-gru/grutlbpurge.c >>>> +++ b/drivers/misc/sgi-gru/grutlbpurge.c >>>> @@ -298,6 +298,7 @@ struct gru_mm_struct *gru_register_mmu_notifier(void) >>>> return ERR_PTR(-ENOMEM); >>>> STAT(gms_alloc); >>>> spin_lock_init(&gms->ms_asid_lock); >>>> + gms->ms_notifier.flags = 0; >>>> gms->ms_notifier.ops = &gru_mmuops; >>>> atomic_set(&gms->ms_refcnt, 1); >>>> init_waitqueue_head(&gms->ms_wait_queue); >>>> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c >>> There is a kzalloc() just above this: >>> gms = kzalloc(sizeof(*gms), GFP_KERNEL); >>> >>> Is that not sufficient to clear the 'flags' field? >>> >> Absolutely, but whether it is better to explicitly document that the mmu >> notifier has cleared flags, i.e. there are no blockable callbacks, is >> another story. I can change it if preferred. > > Actually I would invert the new flag, in other words specify that an MMU > notifier will never sleep. > > The first reason is that we have 8 blocking notifiers and 5 not blocking if I > counted right. So it is actually more common to sleep than not to. > > The second reason is to be conservative and assume the worst, e.g. that the > flag is forgotten when a new notifier is added.
I agree. Some out of tree module might forget to set the flags. Although you don't need to fix out of tree modules, as a troubleshooting staff at a support center, I want to be able to identify the careless module. I guess specifying the flags at register function would be the best, for an attempt to call register function without knowing this change will simply results in a build failure.
