On 05/23/2017 11:21 AM, zhong jiang wrote: > 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. Try applying it then, there's good chance the error and crash will go away. Even if your workload doesn't actually run any madvise(MADV_DONTNEED). > 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? IIRC it's "unstable" wrt possible none->huge->none transition. But once we've seen it's a regular pmd via pmd_trans_unstable(), we're safe as a transition from regular pmd can't happen. > 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> > -- 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>
