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b=lTlJ4Wu+M95u14eDIEgbeePfnTOioVhPOq8hrYMLclOeCve2higYszBR5GdoE7/Vv eL4fXmw9Z4Nd/Wbh8O27k3Pe8jBrbJyZtqcnlPKKKkrWuvcgC6UM/Qd+V3kARn9O68 nQPgbAYzl2OG2/HiXhjvlDAbtrHUuxyqQYo4T6nRr8LTprhsRYpz4kmK76FoWFdfOj PJTD1/WhoAccxq7HElCVcPqSakTnr/Oza9Pg7pu62svNrVdj64QvPC0w0cKIyJ5rzH vRlWMlGlvBvA5T8BTWIyFLEaCVjzfH31lmo19uxx/b1scTA0JoQxz5s92GgkvcOWo9 Pab0i7KlNOBUA== Date: Wed, 26 Aug 2026 09:42:14 +0100 From: "Lorenzo Stoakes (ARM)" To: Vernon Yang Cc: akpm@linux-foundation.org, david@kernel.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, zokeefe@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Vernon Yang Subject: Re: [PATCH v3 2/3] mm: khugepaged: fix folio is used after pte_unmap_unlock() Message-ID: References: <20260824092935.73892-1-vernon2gm@gmail.com> <20260824092935.73892-3-vernon2gm@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A01361C0007 X-Stat-Signature: p3e4thbjq45m1g6kn9mg65xedh511zsr X-Rspam-User: X-HE-Tag: 1787733741-724985 X-HE-Meta: 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 Wphe7x5L +OCrXIryQ1qpNztlDukc7mycSSs0ySF9ViLlGS4ET49LPsiASwTb67ANLe4LzMJA9yjCmJVMzwxULIPRtCk24jT1nsrRj1imuD6HfN0m//UPTPIz/cGmSBEi8XIypdtc8MjmkNvwMtsRbj2a1syp832GImdhiBxKnd2XzgYYGch86t0BCH9bsrR5K/SOrKmaOXsUoPzyD4diUdHSJNYrbkiPtdITXCCcFDMGInF44Y4JdTiCLxnfbGJR0KW18PmCcxKlYScsyYFiuB0kMfzHcnTAkiEfH5yEkGgGIEHjK4lDwWlrjaWN9Zh1it2vUiVlDzf8h Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 26, 2026 at 09:12:52AM +0100, Lorenzo Stoakes (ARM) wrote: > On Mon, Aug 24, 2026 at 05:29:34PM +0800, Vernon Yang wrote: > > From: Vernon Yang > > > > After the page table lock has dropped, the folio can be freed > > concurrently. The trace_mm_khugepaged_scan_pmd() is left with > > a dangling folio pointer. > > > > So using the folio_pfn() before dropping the page table lock, > > closing use-after-free window. > > > > Fixes: 7d2eba0557c1 ("mm: add tracepoint for scanning pages") > > Cc: stable@vger.kernel.org > > Signed-off-by: Vernon Yang > > --- > > include/trace/events/huge_memory.h | 6 +++--- > > mm/khugepaged.c | 5 ++++- > > 2 files changed, 7 insertions(+), 4 deletions(-) > > > > diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > > index 7b526528f85b..fa828967e1fb 100644 > > --- a/include/trace/events/huge_memory.h > > +++ b/include/trace/events/huge_memory.h > > @@ -55,10 +55,10 @@ SCAN_STATUS > > > > TRACE_EVENT(mm_khugepaged_scan_pmd, > > > > - TP_PROTO(struct mm_struct *mm, struct folio *folio, > > + TP_PROTO(struct mm_struct *mm, unsigned long pfn, > > int referenced, int none_or_zero, int status, int unmapped), > > > > - TP_ARGS(mm, folio, referenced, none_or_zero, status, unmapped), > > + TP_ARGS(mm, pfn, referenced, none_or_zero, status, unmapped), > > > > TP_STRUCT__entry( > > __field(struct mm_struct *, mm) > > @@ -71,7 +71,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd, > > > > TP_fast_assign( > > __entry->mm = mm; > > - __entry->pfn = folio ? folio_pfn(folio) : -1; > > + __entry->pfn = pfn; > > __entry->referenced = referenced; > > __entry->none_or_zero = none_or_zero; > > __entry->status = status; > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index 00337405c0e0..4e0fca5942dd 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -1618,6 +1618,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > > enum scan_result result = SCAN_FAIL; > > struct page *page = NULL; > > struct folio *folio = NULL; > > + unsigned long pfn = -1; > > pfn_t please. Disregard :) With David's suggestion applied: Acked-by: Lorenzo Stoakes (ARM) > > > unsigned long addr; > > unsigned long enabled_orders; > > spinlock_t *ptl; > > @@ -1780,6 +1781,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > > result = SCAN_SUCCEED; > > } > > out_unmap: > > + if (folio) > > + pfn = folio_pfn(folio); > > And +1 to David on ensuring this is reset to NULL appropriately. > > > pte_unmap_unlock(pte, ptl); > > if (result == SCAN_SUCCEED) { > > /* collapse_huge_page() expects the lock to be dropped before calling */ > > @@ -1790,7 +1793,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > > *lock_dropped = true; > > } > > out: > > - trace_mm_khugepaged_scan_pmd(mm, folio, referenced, > > + trace_mm_khugepaged_scan_pmd(mm, pfn, referenced, > > none_or_zero, result, unmapped); > > return result; > > } > > -- > > 2.53.0 > > > > -- > Cheers, Lorenzo -- Cheers, Lorenzo