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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Sep 2025 06:22:01.0758 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 03db5c18-24be-4a09-deab-08ddf3570406 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB5PEPF00014B94.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: VE1PR08MB5664 X-Stat-Signature: cwpd5cfrcm4jq63snf34msuzoep1zipo X-Rspam-User: X-Rspamd-Queue-Id: EB8D9180003 X-Rspamd-Server: rspam04 X-HE-Tag: 1757830927-893959 X-HE-Meta: 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 53pIq6TG 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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 14/09/25 5:30 am, Wei Yang wrote: > When using mm_slot in ksm/khugepaged, there is code snip like: > > slot =3D mm_slot_lookup(mm_slots_hash, mm); > mm_slot =3D 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. Shouldn't you fix the code for the case when you can't find the slot in the hashtable, i.e slot =3D=3D NULL? Like, if (!slot) return. What you are currently doing is just ensuring that if slot =3D=3D NULL, the= n we get a legal value of mm_slot, and since the code then operates on the basis of mm_slot, everything will work fine. I really think this is a workaround to the real issue that you got slot =3D=3D NULL :) > > Current code works since mm_slot is the first element, but make sure it > won't be disturbed. > > Signed-off-by: Wei Yang > --- > mm/khugepaged.c | 5 ++++- > mm/ksm.c | 5 ++++- > 2 files changed, 8 insertions(+), 2 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index af5f5c80fe4e..668e74ad33b7 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -108,7 +108,7 @@ struct collapse_control { > * @slot: hash lookup from mm to mm_slot > */ > struct khugepaged_mm_slot { > - struct mm_slot slot; > + struct mm_slot slot; /* keep it the first element */ > }; > > /** > @@ -2382,6 +2382,9 @@ static unsigned int khugepaged_scan_mm_slot(unsigne= d int pages, int *result, > struct vm_area_struct *vma; > int progress =3D 0; > > + BUILD_BUG_ON_MSG(mm_slot_entry(NULL, struct khugepaged_mm_slot, slo= t), > + "slot should be the first element"); > + > VM_BUG_ON(!pages); > lockdep_assert_held(&khugepaged_mm_lock); > *result =3D SCAN_FAIL; > diff --git a/mm/ksm.c b/mm/ksm.c > index 2ef29802a49b..0d486dbdf7d3 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -124,7 +124,7 @@ typedef u8 rmap_age_t; > * @rmap_list: head for this mm_slot's singly-linked list of rmap_items > */ > struct ksm_mm_slot { > - struct mm_slot slot; > + struct mm_slot slot; /* keep it the first element */ > struct ksm_rmap_item *rmap_list; > }; > > @@ -3842,6 +3842,9 @@ static int __init ksm_init(void) > struct task_struct *ksm_thread; > int err; > > + BUILD_BUG_ON_MSG(mm_slot_entry(NULL, struct ksm_mm_slot, slot), > + "slot should be the first element"); > + > /* The correct value depends on page size and endianness */ > zero_checksum =3D calc_checksum(ZERO_PAGE(0)); > /* Default to false for backwards compatibility */ IMPORTANT NOTICE: The contents of this email and any attachments are confid= ential and may also be privileged. If you are not the intended recipient, p= lease notify the sender immediately and do not disclose the contents to any= other person, use it for any purpose, or store or copy the information in = any medium. Thank you.