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t=1786983608; bh=BwmBPA0cmpr0pww4s+vEVGEC63NoNEq70yV7x2DU3f0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=K/lE1v/eySVjx+rC2sXxm6SLXW94ZMm218ziXfKDfGjLCAEm76QEtrWEkhZTX8+PM epjC6DfaGpME43QZEc0wfNXeeBFCGAmKrxb4QOKgvqrPp/cEop7Y2lEVtroYPtZ6V6 IXK+WdZfYjHU48VoRpNdWw0NO4hKb/HTqeZmgosVts6DGxRewARn//GH4xn20ZJHjg VOEUZxK56MCqVCsxhH6bugj1fzpTy5FOc66qhDw3Z2DE1hMECWnpySOH+Dd5ldoA67 wtLTOm2spBn4HB0owjypAfnC7cbNnU5uXLpgMVgveNjHt5DtEgwTIZN+meI6CkluH6 hxdl+R+Gem8CA== Message-ID: Date: Mon, 17 Aug 2026 18:20:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm: khugepaged: fix folio is used after pte_unmap_unlock() To: "Lorenzo Stoakes (ARM)" , Vernon Yang Cc: akpm@linux-foundation.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, Vernon Yang , stable@vger.kernel.org References: <20260815051924.194810-1-vernon2gm@gmail.com> <20260815051924.194810-3-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-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 55CBBC0004 X-Stat-Signature: b7o4pt3c4xkwtfpzyztzb8fhrpmo3dc6 X-HE-Tag: 1786983609-533693 X-HE-Meta: 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 sFJw+w2p 0+LvfDvl3yU1ys6gVDLsC2bL2h5BII5X3EHDzfml1vtQZIqpyc3YzgJ01EohwhUz8w9UebRd/QzM3tkn9Xlln8TewjRNiMW5HDEph7QVTsXhtnwUo22QzwlU6eGSJQffyN3/X34GmnGffIjvqc5ZfCH5Y4FC3dqg7eKWL8SPjlXrfGJyEslkf2sbXoxalsZcdyQAo1TtnVoaWktVXxLc/fv2X01n9sB46UsqQIBmYiF1CtQjckHb0P0xh+RMpfBl3KiGB8ysK6MdDMfS5RzUM+NbppodJQzsGNC23zUi9qcEGjMLaULD3EQ0HUzqCoVKJWSlmbSQqNurac2Y= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/17/26 18:11, Lorenzo Stoakes (ARM) wrote: > On Sat, Aug 15, 2026 at 01:19:23PM +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 | 4 +++- >> 2 files changed, 6 insertions(+), 4 deletions(-) >> >> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h >> index d3572d4ef453..5dc71d292f47 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 e7830761d3a2..7c8c48577408 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -1603,6 +1603,7 @@ 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; >> @@ -1778,6 +1779,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, >> result = SCAN_SUCCEED; >> } >> out_unmap: >> + pfn = folio ? folio_pfn(folio) : -1; >> pte_unmap_unlock(pte, ptl); >> if (result == SCAN_SUCCEED) { >> /* collapse_huge_page expects the lock to be dropped before calling */ >> @@ -1788,7 +1790,7 @@ 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, > > Same comment as 1/3 I don't see why we should be storing a pfn value used > nowhere else just for tracing. I prefer it that way. Even if just for tracing. :) -- Cheers, David