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Date:   Tue, 14 Jun 2022 08:13:52 -0700
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc:     Ying Huang <ying.huang@intel.com>, linux-mm@kvack.org,
        akpm@linux-foundation.org, Wei Xu <weixugc@google.com>,
        Greg Thelen <gthelen@google.com>,
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        Brice Goglin <brice.goglin@gmail.com>,
        Michal Hocko <mhocko@kernel.org>,
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        Alistair Popple <apopple@nvidia.com>,
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        Feng Tang <feng.tang@intel.com>,
        Jagdish Gediya <jvgediya@linux.ibm.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
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        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH v6 01/13] mm/demotion: Add support for explicit memory
 tiers
Message-ID: <20220614151352.6ykunpu3q2e7twmv@offworld>
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        Dan Williams <dan.j.williams@intel.com>,
        Feng Tang <feng.tang@intel.com>,
        Jagdish Gediya <jvgediya@linux.ibm.com>,
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>> memory_tier_lock isn't held to call register_memory_tier() in this
>> patch.  That will cause confusion.
>
>will this help to explain this better
>modified   mm/memory-tiers.c
>@@ -151,6 +151,11 @@ static void insert_memory_tier(struct memory_tier *memtier)
> 	struct list_head *ent;
> 	struct memory_tier *tmp_memtier;
>
>+	if (IS_ENABLED(CONFIG_DEBUG_VM) && !mutex_is_locked(&memory_tier_lock)) {
>+		WARN_ON_ONCE(1);
>+		return;
>+	}

Why not just use lockdep here instead?