From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 379B77E for ; Thu, 7 Dec 2023 00:13:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="h1N6lD4p" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A831FC433CB; Thu, 7 Dec 2023 00:13:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1701908006; bh=2zpaHtZor9sLB7UMb+Hwt1DCdR/acDreEKpsJpXc348=; h=Date:To:From:Subject:From; b=h1N6lD4p8p5G+Usgwm+ZJUcAdp16AcAi1BdhD+MKrMqapeBHb1u+IvXB1Ccr0GvTg AG+FvoQwCt/41L02bNRlKQUOL/ikea8zhJi9RjjI1s5CkdSiZKIi1KMApf+a8qHEji eIfWXfwWxt8q6Ii93P0kbqoAMaXSYhA9jd+eRvLs= Date: Wed, 06 Dec 2023 16:13:26 -0800 To: mm-commits@vger.kernel.org,willy@infradead.org,stable@vger.kernel.org,kirill.shutemov@linux.intel.com,jose.pekkarinen@foxhound.fi,jannh@google.com,david@redhat.com,hughd@google.com,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] mm-fix-oops-when-filemap_map_pmd-without-prealloc_pte.patch removed from -mm tree Message-Id: <20231207001326.A831FC433CB@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm: fix oops when filemap_map_pmd() without prealloc_pte has been removed from the -mm tree. Its filename was mm-fix-oops-when-filemap_map_pmd-without-prealloc_pte.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Hugh Dickins Subject: mm: fix oops when filemap_map_pmd() without prealloc_pte Date: Fri, 17 Nov 2023 00:49:18 -0800 (PST) syzbot reports oops in lockdep's __lock_acquire(), called from __pte_offset_map_lock() called from filemap_map_pages(); or when I run the repro, the oops comes in pmd_install(), called from filemap_map_pmd() called from filemap_map_pages(), just before the __pte_offset_map_lock(). The problem is that filemap_map_pmd() has been assuming that when it finds pmd_none(), a page table has already been prepared in prealloc_pte; and indeed do_fault_around() has been careful to preallocate one there, when it finds pmd_none(): but what if *pmd became none in between? My 6.6 mods in mm/khugepaged.c, avoiding mmap_lock for write, have made it easy for *pmd to be cleared while servicing a page fault; but even before those, a huge *pmd might be zapped while a fault is serviced. The difference in symptomatic stack traces comes from the "memory model" in use: pmd_install() uses pmd_populate() uses page_to_pfn(): in some models that is strict, and will oops on the NULL prealloc_pte; in other models, it will construct a bogus value to be populated into *pmd, then __pte_offset_map_lock() oops when trying to access split ptlock pointer (or some other symptom in normal case of ptlock embedded not pointer). Link: https://lore.kernel.org/linux-mm/20231115065506.19780-1-jose.pekkarinen@foxhound.fi/ Link: https://lkml.kernel.org/r/6ed0c50c-78ef-0719-b3c5-60c0c010431c@google.com Fixes: f9ce0be71d1f ("mm: Cleanup faultaround and finish_fault() codepaths") Signed-off-by: Hugh Dickins Reported-and-tested-by: syzbot+89edd67979b52675ddec@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/0000000000005e44550608a0806c@google.com/ Reviewed-by: David Hildenbrand Cc: Jann Horn , Cc: José Pekkarinen Cc: Kirill A. Shutemov Cc: Matthew Wilcox (Oracle) Cc: [5.12+] Signed-off-by: Andrew Morton --- mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/filemap.c~mm-fix-oops-when-filemap_map_pmd-without-prealloc_pte +++ a/mm/filemap.c @@ -3371,7 +3371,7 @@ static bool filemap_map_pmd(struct vm_fa } } - if (pmd_none(*vmf->pmd)) + if (pmd_none(*vmf->pmd) && vmf->prealloc_pte) pmd_install(mm, vmf->pmd, &vmf->prealloc_pte); return false; _ Patches currently in -mm which might be from hughd@google.com are