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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 May 2025 10:08:27.0520 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9e225647-7f31-43e0-ebf8-08dd99189862 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: AMS1EPF00000048.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAWPR08MB11087 X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C2CAC20007 X-Stat-Signature: przg18y3uigp5nfrfk9kkpnem8cn7w4x X-Rspam-User: X-HE-Tag: 1747908512-359139 X-HE-Meta: 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 GfAwOZfK WZcLDR9/IpHM+keR182G1fOvGk0zizVIHdQ9KOB3HNOLIElgww2VWJPZOEHtAlR6lYkAmvVP2sB9k2zpbLXEzxePgNtFNMhWdNJJW 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 22/05/25 3:04 pm, Shivank Garg wrote: > folio_mapcount() checks folio_test_large() before proceeding to It is not very clear in the description, where is this folio_mapcount() call present? Are you talking about is_refcount_suitable()? > folio_large_mapcount(), but there exists a race window where a folio > could be split between these checks which triggered the > VM_WARN_ON_FOLIO(!folio_test_large(folio), folio) in > folio_large_mapcount(). > > Take a temporary folio reference in hpage_collapse_scan_file() to prevent > races with concurrent folio splitting/freeing. This prevent potential > incorrect large folio detection. > > Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@google.com > Fixes: 05c5323b2a34 ("mm: track mapcount of large folios in single value") > Suggested-by: David Hildenbrand > Signed-off-by: Shivank Garg > --- > mm/khugepaged.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index cc945c6ab3bd..6e8902f9d88c 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2295,6 +2295,17 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > continue; > } > > + if (!folio_try_get(folio)) { > + xas_reset(&xas); > + continue; > + } > + > + if (unlikely(folio != xas_reload(&xas))) { > + folio_put(folio); > + xas_reset(&xas); > + continue; > + } > + > if (folio_order(folio) == HPAGE_PMD_ORDER && > folio->index == start) { > /* Maybe PMD-mapped */ > @@ -2305,23 +2316,27 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > * it's safe to skip LRU and refcount checks before > * returning. > */ > + folio_put(folio); > break; > } > > node = folio_nid(folio); > if (hpage_collapse_scan_abort(node, cc)) { > result = SCAN_SCAN_ABORT; > + folio_put(folio); > break; > } > cc->node_load[node]++; > > if (!folio_test_lru(folio)) { > result = SCAN_PAGE_LRU; > + folio_put(folio); > break; > } > > if (!is_refcount_suitable(folio)) { > result = SCAN_PAGE_COUNT; > + folio_put(folio); > break; > } > > @@ -2333,6 +2348,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > */ > > present += folio_nr_pages(folio); > + folio_put(folio); > > if (need_resched()) { > xas_pause(&xas);