On Wed, Feb 03, 2021 at 03:41:37AM -0500, Miaohe Lin wrote: > 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. > 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)); This is not a complex condition. We're in the huge PMD handling case and we're looking at a PMD which either isn't present or isn't huge. It might be useful to print out the PMD in such a case, but splitting this into the two cases of pmd-not-present and pmd-isn't-huge isn't particularly useful. I think you know that, or you wouldn't feel the need to put in a comment explaining it!
