On Tue, Jun 21, 2016 at 10:05:56PM +0800, zhongjiang wrote: > From: zhong jiang <[email protected]> > > with great pressure, I run some test cases. As a result, I found > that the THP is not freed, it is detected by check_mm(). > > BUG: Bad rss-counter state mm:ffff8827edb70000 idx:1 val:512 > > Consider the following race : > > CPU0 CPU1 > __handle_mm_fault() > wp_huge_pmd() > do_huge_pmd_wp_page() > pmdp_huge_clear_flush_notify() > (pmd_none = true) > exit_mmap() > unmap_vmas() > zap_pmd_range() > > pmd_none_or_trans_huge_or_clear_bad() > (result in memory leak) > set_pmd_at() > > because of CPU0 have allocated huge page before pmdp_huge_clear_notify, > and it make the pmd entry to be null. Therefore, The memory leak can occur. > > The patch fix the scenario that the pmd entry can lead to be null.
I don't think the scenario is possible. exit_mmap() called when all mm users have gone, so no parallel threads exist. -- Kirill A. Shutemov
