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Wed, 24 Sep 2025 05:35:10 -0400 (EDT) Date: Wed, 24 Sep 2025 10:35:07 +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, Dan Carpenter Subject: Re: [Patch v3 1/2] mm/ksm: get mm_slot by mm_slot_entry() when slot is !NULL Message-ID: <27storxu4seijr5smul3xx7pofe45ittjrchii3jtwbntalsiy@2cu3wf42drwa> References: <20250924004854.29889-1-richard.weiyang@gmail.com> <20250924004854.29889-2-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250924004854.29889-2-richard.weiyang@gmail.com> X-Stat-Signature: bim6jcnxa1ehn8oi3g97i6pbq4t4bhjo X-Rspam-User: X-Rspamd-Queue-Id: 245B4140008 X-Rspamd-Server: rspam10 X-HE-Tag: 1758706512-858397 X-HE-Meta: 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 vrGwS9Gz 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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 Wed, Sep 24, 2025 at 12:48:53AM +0000, Wei Yang wrote: > Patch series "mm_slot: fix the usage of mm_slot_entry", v2. > > When using mm_slot in ksm, there is code like: > > slot = mm_slot_lookup(mm_slots_hash, mm); > mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); > if (mm_slot && ..) { > } > > The mm_slot_entry() won't return a valid value if slot is NULL generally. > But currently it works since slot is the first element of struct > ksm_mm_slot. > > To reduce the ambiguity and make it robust, access mm_slot_entry() when > slot is !NULL. > > Signed-off-by: Wei Yang > Acked-by: David Hildenbrand > Reviewed-by: Dev Jain > Reviewed-by: Lance Yang > Cc: Kiryl Shutsemau > Cc: xu xin > Cc: Dan Carpenter > > --- > v3: > * fix uninitialized mm_slot > --- > mm/ksm.c | 22 ++++++++++++---------- > 1 file changed, 12 insertions(+), 10 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 2dbe92e3dd52..c00a21800067 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -2921,7 +2921,7 @@ int __ksm_enter(struct mm_struct *mm) > > void __ksm_exit(struct mm_struct *mm) > { > - struct ksm_mm_slot *mm_slot; > + struct ksm_mm_slot *mm_slot = NULL; > struct mm_slot *slot; > int easy_to_free = 0; > > @@ -2936,15 +2936,17 @@ void __ksm_exit(struct mm_struct *mm) > > spin_lock(&ksm_mmlist_lock); > slot = mm_slot_lookup(mm_slots_hash, mm); > - mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); > - if (mm_slot && ksm_scan.mm_slot != mm_slot) { > - if (!mm_slot->rmap_list) { > - hash_del(&slot->hash); > - list_del(&slot->mm_node); > - easy_to_free = 1; > - } else { > - list_move(&slot->mm_node, > - &ksm_scan.mm_slot->slot.mm_node); > + if (slot) { > + mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); > + if (ksm_scan.mm_slot != mm_slot) { > + if (!mm_slot->rmap_list) { > + hash_del(&slot->hash); > + list_del(&slot->mm_node); > + easy_to_free = 1; > + } else { > + list_move(&slot->mm_node, > + &ksm_scan.mm_slot->slot.mm_node); > + } Indent level gets extreme. Any reason not to fold slot check inside mm_slot_entry() as I suggested on early version. > } > } > spin_unlock(&ksm_mmlist_lock); > -- > 2.34.1 > -- Kiryl Shutsemau / Kirill A. Shutemov