[PATCH 1/2] mm/vmalloc: acquire init_mm read lock on huge vmap promotion

[Mike Rapoport]

On Fri, Jul 10, 2026 at 11:49:18AM +0100, Lorenzo Stoakes wrote:
> Currently there is a nasty race between ptdump and vmap when attempting to
> map a huge P4D, PMD or PUD entry.
>
> This patch resolves the issue by simply having
> vmap_try_huge_[p4d,pud,pmd]() hold the mmap read lock on init_mm while
> invoking [p4d,pud,pmd]_free_[pud,pmd,pte]_page() and
> [p4d,pud,pmd]_set_huge().
> 
> Fixes: b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page table")
> Cc: <stable at vger.kernel.org>
> Reported-by: syzbot+fd95a72470f5a44e464c at syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/6a287988.39669fcc.33b062.00a0.GAE@google.com/T/
> Link: https://lore.kernel.org/linux-mm/20260706203128.162335-1-devnexen@gmail.com/
> Signed-off-by: Lorenzo Stoakes <ljs at kernel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt at kernel.org>

> ---
>  include/linux/mmap_lock.h |  1 +
>  mm/pagewalk.c             | 22 +++++++++++----------
>  mm/vmalloc.c              | 50 ++++++++++++++++++++++++++++++++++++++---------
>  3 files changed, 54 insertions(+), 19 deletions(-)

-- 
Sincerely yours,
Mike.