On 2017/5/23 0:51, Vlastimil Babka wrote: > On 05/20/2017 05:01 AM, zhong jiang wrote: >> On 2017/5/20 10:40, Hugh Dickins wrote: >>> On Sat, 20 May 2017, Xishi Qiu wrote: >>>> Here is a bug report form redhat: https://bugzilla.redhat.com/show_bug.cgi?id=1305620 >>>> And I meet the bug too. However it is hard to reproduce, and >>>> 624483f3ea82598("mm: rmap: fix use-after-free in __put_anon_vma") is not help. >>>> >>>> From the vmcore, it seems that the page is still mapped(_mapcount=0 and _count=2), >>>> and the value of mapping is a valid address(mapping = 0xffff8801b3e2a101), >>>> but anon_vma has been corrupted. >>>> >>>> Any ideas? >>> Sorry, no. I assume that _mapcount has been misaccounted, for example >>> a pte mapped in on top of another pte; but cannot begin tell you where >>> in Red Hat's kernel-3.10.0-229.4.2.el7 that might happen. >>> >>> Hugh >>> >>> . >>> >> Hi, Hugh >> >> I find the following message from the dmesg. >> >> [26068.316592] BUG: Bad rss-counter state mm:ffff8800a7de2d80 idx:1 val:1 >> >> I can prove that the __mapcount is misaccount. when task is exited. the rmap >> still exist. > Check if the kernel in question contains this commit: ad33bb04b2a6 ("mm: > thp: fix SMP race condition between THP page fault and MADV_DONTNEED") HI, Vlastimil I miss the patch. when I read the patch. I find the following issue. but I am sure it is right. if (unlikely(pmd_trans_unstable(pmd))) return 0; /* * A regular pmd is established and it can't morph into a huge pmd * from under us anymore at this point because we hold the mmap_sem * read mode and khugepaged takes it in write mode. So now it's * safe to run pte_offset_map(). */ pte = pte_offset_map(pmd, address); after pmd_trans_unstable call, without any protect method. by the comments, it think the pte_offset_map is safe. before pte_offset_map call, it still may be unstable. it is possible? Thanks zhongjiang >> Thanks >> zhongjiang >> >> -- >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> the body to majordomo@xxxxxxxxx. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> >> > > . > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
