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SubjectRe: [PATCH RFC 00/15] decouple pagefault_disable() from preempt_disable()
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.

>
> ..
>

> This series therefore does 2 things:
>
>
> 1. Decouple pagefault_disable() from preempt_enable()
>
> ...
>
> 2. Reenable might_sleep() checks for might_fault()

All seems sensible to me. pagefault_disabled has to go into the
task_struct (rather than being per-cpu) because
pagefault_disabled_inc() doesn't disable preemption, yes?



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