The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 9aa1345d66b8132745ffb99b348b1492088da9e2 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2023120945-citizen-library-9f46@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
Possible dependencies:
9aa1345d66b8 ("mm: fix oops when filemap_map_pmd() without prealloc_pte") 03c4f20454e0 ("mm: introduce pmd_install() helper")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 9aa1345d66b8132745ffb99b348b1492088da9e2 Mon Sep 17 00:00:00 2001 From: Hugh Dickins hughd@google.com Date: Fri, 17 Nov 2023 00:49:18 -0800 Subject: [PATCH] mm: fix oops when filemap_map_pmd() without prealloc_pte MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit
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@foxh... 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 hughd@google.com Reported-and-tested-by: syzbot+89edd67979b52675ddec@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/0000000000005e44550608a0806c@google.com/ Reviewed-by: David Hildenbrand david@redhat.com Cc: Jann Horn jannh@google.com, Cc: José Pekkarinen jose.pekkarinen@foxhound.fi Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: stable@vger.kernel.org [5.12+] Signed-off-by: Andrew Morton akpm@linux-foundation.org
diff --git a/mm/filemap.c b/mm/filemap.c index 32eedf3afd45..f1c8c278310f 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3371,7 +3371,7 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio, } }
- if (pmd_none(*vmf->pmd)) + if (pmd_none(*vmf->pmd) && vmf->prealloc_pte) pmd_install(mm, vmf->pmd, &vmf->prealloc_pte);
return false;