mm/pgtable-generic.c: optimize the VM_BUG_ON condition in pmdp_huge_clear_flush()

The developer will have trouble figuring out why the BUG actually
triggered when there is a complex expression in the VM_BUG_ON.  Because we
can only identify the condition triggered BUG via line number provided by
VM_BUG_ON.  Optimize this by spliting such a complex expression into two
simple conditions.

Link: https://lkml.kernel.org/r/20210203084137.25522-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index fa1375f3e3b2457dae2c2cf56743baf288b2e54d..c2210e1cdb51561aba670f6d717b7c8db98c0fb1 100644 (file)
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -135,8 +135,9 @@ pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
 {
        pmd_t pmd;
        VM_BUG_ON(address & ~HPAGE_PMD_MASK);
-       VM_BUG_ON(!pmd_present(*pmdp) || (!pmd_trans_huge(*pmdp) &&
-                                         !pmd_devmap(*pmdp)));
+       VM_BUG_ON(!pmd_present(*pmdp));
+       /* Below assumes pmd_present() is true */
+       VM_BUG_ON(!pmd_trans_huge(*pmdp) && !pmd_devmap(*pmdp));
        pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
        flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
        return pmd;