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    SubjectPerformance Question: BUG_ON vs. WARN_ON_ONCE
    I was porting the -rt branch to the latest -mm kernel and encountered
    a bug. The
    replace-bugon-by-warn-on.patch patch make the following change:

    diff --git a/18f7d025bb2e5762fd4063cce0b6e2342475c55c:arch/x86/mm/highmem_32.c
    b/db090b52f9d2f9088a4ff9bce530e3c234c8e3af:arch/x86/mm/highmem_32.c
    index 165c871ba9af0211e0c939e0bc2212750d4bf39f..402ecdd04d7818fd24e921c94b698faa19383b71
    100644
    --- a/18f7d025bb2e5762fd4063cce0b6e2342475c55c:arch/x86/mm/highmem_32.c
    +++ b/db090b52f9d2f9088a4ff9bce530e3c234c8e3af:arch/x86/mm/highmem_32.c
    @@ -84,7 +84,7 @@ void *kmap_atomic_prot(struct page *page, enum
    km_type type, pgprot_t prot)

    idx = type + KM_TYPE_NR*smp_processor_id();
    vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
    - BUG_ON(!pte_none(*(kmap_pte-idx)));
    + WARN_ON_ONCE(!pte_none(*(kmap_pte-idx)));
    set_pte(kmap_pte-idx, mk_pte(page, prot));
    arch_flush_lazy_mmu_mode();

    However, this causes the kernel to crash or oops under certain loads.
    Reverting this change makes the error go away. Is there any sort of
    performance difference between BUG_ON and WARN_ON_ONCE, I figure the
    change was for a reason so I am wondering what will result from this
    change. Any info would be appreciated.
    -Ryan


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