Messages in this thread Patch in this message | | | Date | Fri, 13 Jan 2023 19:04:14 +0000 | From | Lorenzo Stoakes <> | Subject | Re: [PATCH -next 5/7] mm: memory: convert wp_page_copy() to use folios |
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On Fri, Jan 13, 2023 at 02:08:36PM +0100, David Hildenbrand wrote: > On 13.01.23 14:01, Marek Szyprowski wrote: > > Hi > > > > On 12.01.2023 09:30, Kefeng Wang wrote: > > > The old_page/new_page are converted to old_folio/new_folio in > > > wp_page_copy(), then replaced related page functions to folio > > > functions. > > > > > > Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com> > > > > This patch, merged into today's linux-next as commit 9ebae00c8e30 ("mm: > > memory: convert wp_page_copy() to use folios"), causes serious stability > > issues on my ARM based test boards. Here is the example of such crash: > > syzbot is also not happy: > > https://lkml.kernel.org/r/000000000000807c7805f2205df1@google.com > > -- > Thanks, > > David / dhildenb >
This also completely broke my qemu environment.
In that thread Willy points out that the issue stems from blindly assigning page_folio(old_page) to old_folio without checking whether it is NULL first, therefore triggering a NULL pointer deref.
A quick fix would be to put in a check (as shown below) which fixes the issue, but as Willy said, I think we should drop this until it can be fixed in a respin.
--- a/mm/memory.c +++ b/mm/memory.c @@ -3044,7 +3044,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) struct vm_area_struct *vma = vmf->vma; struct mm_struct *mm = vma->vm_mm; struct page *old_page = vmf->page; - struct folio *old_folio = page_folio(old_page); + struct folio *old_folio = old_page ? page_folio(old_page) : NULL;
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