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Date:   Fri, 24 Aug 2018 18:40:03 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Jerome Glisse <jglisse@redhat.com>
Cc:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
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        Alex Deucher <alexander.deucher@amd.com>,
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        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
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Subject: Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers
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On Fri 24-08-18 11:12:40, Jerome Glisse wrote:
[...]
> I am fine with Michal patch, i already said so couple month ago first time
> this discussion did pop up, Michal you can add:
> 
> Reviewed-by: J?r?me Glisse <jglisse@redhat.com>

So I guess the below is the patch you were talking about?

From f7ac75277d526dccd011f343818dc6af627af2af Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Fri, 24 Aug 2018 15:32:24 +0200
Subject: [PATCH] mm, mmu_notifier: be explicit about range invalition
 non-blocking mode

If invalidate_range_start is called for !blocking mode then all
callbacks have to guarantee they will no block/sleep. The same obviously
applies to invalidate_range_end because this operation pairs with the
former and they are called from the same context. Make sure this is
appropriately documented.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/mmu_notifier.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 133ba78820ee..698e371aafe3 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -153,7 +153,9 @@ struct mmu_notifier_ops {
 	 *
 	 * If blockable argument is set to false then the callback cannot
 	 * sleep and has to return with -EAGAIN. 0 should be returned
-	 * otherwise.
+	 * otherwise. Please note that if invalidate_range_start approves
+	 * a non-blocking behavior then the same applies to
+	 * invalidate_range_end.
 	 *
 	 */
 	int (*invalidate_range_start)(struct mmu_notifier *mn,
-- 
2.18.0

-- 
Michal Hocko
SUSE Labs