Re: [PATCH 2/3] mm, notifier: Catch sleeping/blocking for !blockable

["Koenig, Christian" <Christian.Koenig@amd.com>]

Am 22.11.18 um 17:51 schrieb Daniel Vetter:
> We need to make sure implementations don't cheat and don't have a
> possible schedule/blocking point deeply burried where review can't
> catch it.
>
> I'm not sure whether this is the best way to make sure all the
> might_sleep() callsites trigger, and it's a bit ugly in the code flow.
> But it gets the job done.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> Cc: linux-mm@kvack.org
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>   mm/mmu_notifier.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> index 59e102589a25..4d282cfb296e 100644
> --- a/mm/mmu_notifier.c
> +++ b/mm/mmu_notifier.c
> @@ -185,7 +185,13 @@ int __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
>   	id = srcu_read_lock(&srcu);
>   	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
>   		if (mn->ops->invalidate_range_start) {
> -			int _ret = mn->ops->invalidate_range_start(mn, mm, start, end, blockable);
> +			int _ret;
> +
> +			if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP) && !blockable)
> +				preempt_disable();
> +			_ret = mn->ops->invalidate_range_start(mn, mm, start, end, blockable);
> +			if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP) && !blockable)
> +				preempt_enable();

Just for the sake of better documenting this how about adding this to 
include/linux/kernel.h right next to might_sleep():

#define disallow_sleeping_if(cond)    for((cond) ? preempt_disable() : 
(void)0; (cond); preempt_disable())

(Just from the back of my head, might contain peanuts and/or hints of 
errors).

Christian.

>   			if (_ret) {
>   				pr_info("%pS callback failed with %d in %sblockable context.\n",
>   						mn->ops->invalidate_range_start, _ret,