Re: [PATCH 3/4] mm, notifier: Catch sleeping/blocking for !blockable

Jerome Glisse
2019-05-21T15:32:00Z

On Mon, May 20, 2019 at 11:39:44PM +0200, Daniel Vetter wrote:
> 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.
>
> Inspired by an i915 patch series which did exactly that, because the
> rules haven't been entirely clear to us.
>
> v2: Use the shiny new non_block_start/end annotations instead of
> abusing preempt_disable/enable.
>
> v3: Rebase on top of Glisse's arg rework.
>
> v4: Rebase on top of more Glisse rework.
>
> 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
> Reviewed-by: Christian König <christian.koenig@amd.com>
> 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 c05e406a7cd7..a09e737711d5 100644
> --- a/mm/mmu_notifier.c
> +++ b/mm/mmu_notifier.c
> @@ -176,7 +176,13 @@ int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
> id = srcu_read_lock(&srcu);
> hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
> if (mn->ops->invalidate_range_start) {
> - int _ret = mn->ops->invalidate_range_start(mn, range);
> + int _ret;
> +
> + if (!mmu_notifier_range_blockable(range))
> + non_block_start();
> + _ret = mn->ops->invalidate_range_start(mn, range);
> + if (!mmu_notifier_range_blockable(range))
> + non_block_end();

This is a taste thing so feel free to ignore it as maybe other
will dislike more what i prefer:

+ if (!mmu_notifier_range_blockable(range)) {
+ non_block_start();
+ _ret = mn->ops->invalidate_range_start(mn, range);
+ non_block_end();
+ } else
+ _ret = mn->ops->invalidate_range_start(mn, range);

If only we had predicate on CPU like on GPU :)

In any case:

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

> if (_ret) {
> pr_info("%pS callback failed with %d in %sblockable context.\n",
> mn->ops->invalidate_range_start, _ret,
> --
> 2.20.1
>