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Mon, 15 Sep 2025 05:39:31 -0400 (EDT) Date: Mon, 15 Sep 2025 10:39:28 +0100 From: Kiryl Shutsemau To: Wei Yang Cc: akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, linux-mm@kvack.org Subject: Re: [PATCH] mm/mm_slot: make sure slot is the first element of its wrapper structure Message-ID: References: <20250914000026.17986-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250914000026.17986-1-richard.weiyang@gmail.com> X-Rspamd-Queue-Id: E393AA0011 X-Stat-Signature: 41hdqne6przkwa1p8ixwog3zjjba7kg9 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1757929174-411884 X-HE-Meta: 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 EI07dnab 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Sep 14, 2025 at 12:00:26AM +0000, Wei Yang wrote: > When using mm_slot in ksm/khugepaged, there is code snip like: > > slot = mm_slot_lookup(mm_slots_hash, mm); > mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); > if (mm_slot && ..) { > } > > This is only valid when mm_slot is the first element of its wrapper > structure, otherwise a NULL slot would converted to a mm_slot with > negative value. And current code thinks it is valid and continue. > > Current code works since mm_slot is the first element, but make sure it > won't be disturbed. Seems excessive for this kind of problem. Why not check slot in mm_slot_entry? diff --git a/mm/mm_slot.h b/mm/mm_slot.h index 83f18ed1c4bd..0de24c490b62 100644 --- a/mm/mm_slot.h +++ b/mm/mm_slot.h @@ -19,7 +19,7 @@ struct mm_slot { }; #define mm_slot_entry(ptr, type, member) \ - container_of(ptr, type, member) + (ptr ? container_of(ptr, type, member) : NULL) static inline void *mm_slot_alloc(struct kmem_cache *cache) { -- Kiryl Shutsemau / Kirill A. Shutemov