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t=1787732089; bh=jc5AoHf2qjE/ikpZjUfB6MnpSBqN1XX0+Zdh1Ro7A4Q=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=gEYJJikc/toz6F8QKezBvlpwgGyWhfluynnS9RhLMjWauJkS61XhCi+K2Vksr8hAV irfSunCZqgGbBgSs3Lr4I9Vx4ardA9nx+pgb/fvWT8ke8hiyZMWU5p6RbSdkPdF/s5 5r6PFfy+CNJkElRqe7mjpXcC3hsI4zVazezxxglECtveJO3aHcdabWELJOx2wdPg5t bDwSj9vqu0VLWeX3bi7PpWuHrZ05rviaJfkuLBMJNcM8H0M02WFb3aYsbSdSnz1ldz F0k63wUZilpSrU1WVU2TKTsPH5KZT66qQ/Mf0W8bRI/RRHU4dNuimyIj8M3m2pi7Zm B9Up3WLdg0eyw== Message-ID: <77412338-b54c-455b-84da-1f39db641c90@kernel.org> Date: Wed, 26 Aug 2026 10:14:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/3] mm: khugepaged: fix folio is used after folio_put/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, stable@vger.kernel.org, Vernon Yang References: <20260824092935.73892-1-vernon2gm@gmail.com> <20260824092935.73892-4-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: rspam10 X-Rspamd-Queue-Id: 66E8C80008 X-Stat-Signature: yy6yxyn86c6f979st46xsqfkawnsqpgh X-HE-Tag: 1787732090-201340 X-HE-Meta: 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 NSjBNsf6 Etkmg0/v4pE+EV1YToG9gIBGPXmmPNThT2sAFyGY/392h4WzxG0pF3ERgoGRSdftyVIYamCwy2S1VkVPq23MSadE4SL5i+6QfO/+dc/rhZdXW8i+EhXrJAjPFgYegE34Pftsc2zwCFp8T+YbF5hWh4j/O95CZzQoGwHFJu6MxsK9UMIc888pkqMU6P/YUkHUlAeqOg5jXNcMAlgEtXd/vuG7x4bXJB2Pn7KrQ7heq9rhMlSNFi0jbUpDkKzSsA6dS52Dpqxp434WXCSzr2HRdkEdTLy4+Do5mkrgCO2S4COT7k7j2BcF1ymldqZPqUuhQGDRmUzYe6uCLKkU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/26/26 10:09, Lorenzo Stoakes (ARM) wrote: > On Mon, Aug 24, 2026 at 05:29:35PM +0800, Vernon Yang wrote: >> From: Vernon Yang >> >> On the rollback path, folio_put() has already dropped the last reference >> of new_folio. On the success path, new_folio is already unlocked and can >> be freed concurrently. The trace_mm_khugepaged_collapse_file() is left >> with a dangling folio pointer. >> >> So using the folio_pfn() before dropping the reference, closing >> use-after-free window. >> >> Fixes: 4c9473e87e75 ("mm/khugepaged: add tracepoint to collapse_file()") >> 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 fa828967e1fb..5fb4d92cfd84 100644 >> --- a/include/trace/events/huge_memory.h >> +++ b/include/trace/events/huge_memory.h >> @@ -211,10 +211,10 @@ TRACE_EVENT(mm_khugepaged_scan_file, >> ); >> >> TRACE_EVENT(mm_khugepaged_collapse_file, >> - TP_PROTO(struct mm_struct *mm, struct folio *new_folio, pgoff_t index, >> + TP_PROTO(struct mm_struct *mm, unsigned long new_pfn, pgoff_t index, >> unsigned long addr, bool is_shmem, struct file *file, >> int nr, int result), >> - TP_ARGS(mm, new_folio, index, addr, is_shmem, file, nr, result), >> + TP_ARGS(mm, new_pfn, index, addr, is_shmem, file, nr, result), >> TP_STRUCT__entry( >> __field(struct mm_struct *, mm) >> __field(unsigned long, hpfn) >> @@ -228,7 +228,7 @@ TRACE_EVENT(mm_khugepaged_collapse_file, >> >> TP_fast_assign( >> __entry->mm = mm; >> - __entry->hpfn = new_folio ? folio_pfn(new_folio) : -1; >> + __entry->hpfn = new_pfn; >> __entry->index = index; >> __entry->addr = addr; >> __entry->is_shmem = is_shmem; >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 4e0fca5942dd..24347f1a94ae 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -2254,6 +2254,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, >> struct address_space *mapping = file->f_mapping; >> struct page *dst; >> struct folio *folio, *tmp, *new_folio; >> + unsigned long new_pfn = -1; > > Nitty but: > > Could we use pfn_t? I don't love that we are inconsistent with that. Note that the monstrosity we called pfn_t no longer exits. :) -- Cheers, David