* Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote: > Am 07.05.2015 um 11:48 schrieb Ingo Molnar: > > > > * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > >> On Wed, 6 May 2015 19:50:24 +0200 David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx> wrote: > >> > >>> As Peter asked me to also do the decoupling in one shot, this is > >>> the new series. > >>> > >>> I recently discovered that might_fault() doesn't call might_sleep() > >>> anymore. Therefore bugs like: > >>> > >>> spin_lock(&lock); > >>> rc = copy_to_user(...); > >>> spin_unlock(&lock); > >>> > >>> would not be detected with CONFIG_DEBUG_ATOMIC_SLEEP. The code was > >>> changed to disable false positives for code like: > >>> > >>> pagefault_disable(); > >>> rc = copy_to_user(...); > >>> pagefault_enable(); > >>> > >>> Whereby the caller wants do deal with failures. > >> > >> hm, that was a significant screwup. I wonder how many bugs we > >> subsequently added. > > > > So I'm wondering what the motivation was to allow things like: > > > > pagefault_disable(); > > rc = copy_to_user(...); > > pagefault_enable(); > > > > and to declare it a false positive? > > > > AFAICS most uses are indeed atomic: > > > > pagefault_disable(); > > ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); > > pagefault_enable(); > > > > so why not make it explicitly atomic again? > > Hmm, I am probably misreading that, but it sound as you suggest to go back > to Davids first proposal > https://lkml.org/lkml/2014/11/25/436 > which makes might_fault to also contain might_sleep. Correct? Yes, but I'm wondering what I'm missing: is there any deep reason for making pagefaults-disabled sections non-atomic? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
