On 13/12/2017 11:26, Tetsuo Handa wrote: > 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. Specifying them in the ops would have the same effect and it would be even better, as you don't have to split the information across two places. Paolo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
