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| author | Jann Horn <jannh@google.com> | 2024-08-13 22:25:22 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2024-09-12 11:12:47 +0200 |
| commit | db978287e908d48b209e374b00d847b2d785e0a9 (patch) | |
| tree | e9b3ceb1cd655fc033b3c6bbd4307100b5640255 /mm | |
| parent | 4679272d5252720746fd9c5465352cbc5665f230 (diff) | |
| download | linux-db978287e908d48b209e374b00d847b2d785e0a9.tar.gz linux-db978287e908d48b209e374b00d847b2d785e0a9.tar.bz2 linux-db978287e908d48b209e374b00d847b2d785e0a9.zip | |
userfaultfd: don't BUG_ON() if khugepaged yanks our page table
commit 4828d207dc5161dc7ddf9a4f6dcfd80c7dd7d20a upstream.
Since khugepaged was changed to allow retracting page tables in file
mappings without holding the mmap lock, these BUG_ON()s are wrong - get
rid of them.
We could also remove the preceding "if (unlikely(...))" block, but then we
could reach pte_offset_map_lock() with transhuge pages not just for file
mappings but also for anonymous mappings - which would probably be fine
but I think is not necessarily expected.
Link: https://lkml.kernel.org/r/20240813-uffd-thp-flip-fix-v2-2-5efa61078a41@google.com
Fixes: 1d65b771bc08 ("mm/khugepaged: retract_page_tables() without mmap or vma lock")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/userfaultfd.c | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index defa5109cc62..335de81ae5d4 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -805,9 +805,10 @@ retry: err = -EFAULT; break; } - - BUG_ON(pmd_none(*dst_pmd)); - BUG_ON(pmd_trans_huge(*dst_pmd)); + /* + * For shmem mappings, khugepaged is allowed to remove page + * tables under us; pte_offset_map_lock() will deal with that. + */ err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, src_addr, flags, &folio); |