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

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Message-ID: <20190521153200.GB3836@redhat.com>
Date:   Tue, 21 May 2019 11:32:00 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Christian König <christian.koenig@....com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 3/4] mm, notifier: Catch sleeping/blocking for !blockable

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@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: "Christian König" <christian.koenig@....com>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: linux-mm@...ck.org
> Reviewed-by: Christian König <christian.koenig@....com>
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.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@...hat.com>


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