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b=JRXBKFWszASHGhmzQvsODRiJHHZB1O2eyOoQcpvC7EZfBv8p20n0oVl8kJFGrrmp+ LsjQHyI6OdhRnUqzcGcKCmKZRLEKY+MUfMXj3+rSkxddYtLT5synKaamVsaqccFRJo GbmyzlKyS0aEGCa5X9gpsCKEQGGgyquVZ5d6FgMoquHMnT8XMFgrH93tWjuBMBoSAv JzN8zrua6lAtTiH2dy20HeijQ+z/eMjm0AhJ7Ur7K2OxtYpWIgHroePsOoiZCs4xNy VH9es3yPHsK7ia6EYhrIDwFi0NkOM+AL++Nogb55H7llIW1pw8Wn/dU126a/397jQm r8ZSw/bkkV2vg== Message-ID: <0bc399df-2555-4378-bee4-eacbff434bdd@kernel.org> Date: Mon, 24 Aug 2026 13:57:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] mm: khugepaged: fix folio is used after pte_unmap_unlock() To: Vernon Yang , akpm@linux-foundation.org, ljs@kernel.org Cc: 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 References: <20260824092935.73892-1-vernon2gm@gmail.com> <20260824092935.73892-3-vernon2gm@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 7C5321C0002 X-Stat-Signature: 4msxoz9aci7f8ayqjupuj8k49uqmrn9w X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1787572642-996982 X-HE-Meta: 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 2WHu1Amw KKvBkA6MsnPv9jiOHdF15sPdDofMP7Sayo3ipLTNZee2cP3K5i8AKBfy5RYHqUMxKnq80CXbytRkxkgccQYfHcbyV0VtyfTes9dR7v4lzWkDT7kM7RcRknB6QVuGa+JTyVgpJqRzkYAy8VUYdxmKukJF9OOf5t+DrJq/0kMnRyrn+OBhVJ5gPoPSYpmyEJ9dT9saDmi7mrvkbA3IeTbZIcqXTTZJYPCSCH20qFsobOyytZ+9ZFl2weKw8wkGdRtfrNow7J2qDFKb5VS43b3FpAh7dohEl89kTsaKTx2z2AsWJXiUb8vLjjXOwjj5eO1sDKeffQynjqUTVwAE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/24/26 11:29, 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; > 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); Should we reset the folio to NULL at the beginning of the loop? Then we really only trace the PFN if it really was problematic. -- Cheers, David