On Fri, Nov 15, 2019 at 11:58:00AM -0800, Andrew Morton wrote: > On Fri, 15 Nov 2019 12:58:08 +0100 Thomas Hellström (VMware) <thomas_os@xxxxxxxxxxxx> wrote: > > > A huge pud page can theoretically be faulted in racing with pmd_alloc() > > in __handle_mm_fault(). That will lead to pmd_alloc() returning an > > invalid pmd pointer. Fix this by adding a pud_trans_unstable() function > > similar to pmd_trans_unstable() and check whether the pud is really stable > > before using the pmd pointer. > > > > Race: > > Thread 1: Thread 2: Comment > > create_huge_pud() Fallback - not taken. > > create_huge_pud() Taken. > > pmd_alloc() Returns an invalid pointer. > > What are the user-visible runtime effects of this change? Data corruption: kernel writes to a huge page thing it's page table. > Is a -stable backport warranted? I believe it is. Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> -- Kirill A. Shutemov
