mm: prevent userfaults to be handled under per-vma lock
Due to the possibility of handle_userfault dropping mmap_lock, avoid fault handling under VMA lock and retry holding mmap_lock. This can be handled more gracefully in the future. Link: https://lkml.kernel.org/r/20230227173632.3292573-28-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Suggested-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@ -5266,6 +5266,15 @@ retry:
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if (!vma_start_read(vma))
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goto inval;
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/*
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* Due to the possibility of userfault handler dropping mmap_lock, avoid
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* it for now and fall back to page fault handling under mmap_lock.
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*/
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if (userfaultfd_armed(vma)) {
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vma_end_read(vma);
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goto inval;
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}
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/* Check since vm_start/vm_end might change before we lock the VMA */
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if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
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vma_end_read(vma);
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