On Sat, Dec 09, 2023 at 01:35:45PM +0100, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> 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@xxxxxxxxxxxxxxx>.
This should do the job. It's not clear to me whether this bug remains
latent on 5.15, so it may not be appropriate to apply. I defer to Hugh.
diff --git a/mm/filemap.c b/mm/filemap.c
index 81e28722edfa..84a5b0213e0e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3209,7 +3209,7 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
}
}
- if (pmd_none(*vmf->pmd)) {
+ if (pmd_none(*vmf->pmd) && vmf->prealloc_pte) {
vmf->ptl = pmd_lock(mm, vmf->pmd);
if (likely(pmd_none(*vmf->pmd))) {
mm_inc_nr_ptes(mm);
> 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@xxxxxxxxxxxxxxx>' --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@xxxxxxxxxx>
> 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@xxxxxxxxxxx/
> Link: https://lkml.kernel.org/r/6ed0c50c-78ef-0719-b3c5-60c0c010431c@xxxxxxxxxx
> Fixes: f9ce0be71d1f ("mm: Cleanup faultaround and finish_fault() codepaths")
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Reported-and-tested-by: syzbot+89edd67979b52675ddec@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/linux-mm/0000000000005e44550608a0806c@xxxxxxxxxx/
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Jann Horn <jannh@xxxxxxxxxx>,
> Cc: José Pekkarinen <jose.pekkarinen@xxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> [5.12+]
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>
> 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;
>
