Messages in this thread | | | Date | Thu, 7 May 2015 11:48:19 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH RFC 00/15] decouple pagefault_disable() from preempt_disable() |
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* Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 6 May 2015 19:50:24 +0200 David Hildenbrand <dahi@linux.vnet.ibm.com> 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?
Thanks,
Ingo
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