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SubjectRe: [PATCH 2/3] inotify: do not BUG on idr entries at inotify destruction


On Tue, 25 Aug 2009, Mikko C. wrote:
>
> I just got this with -rc7, but it doesn't look related to what I was having
> before:
>
> BUG: Bad page map in process kio_thumbnail pte:ffff88006cc99128 pmd:6d3b1067
> addr:00007f9d4e3a5000 vm_flags:08000070 anon_vma:(null)
> mapping:ffff88007abe21a0 index:200
> vma->vm_ops->fault: filemap_fault+0x0/0x460
> vma->vm_file->f_op->mmap: ext4_file_mmap+0x0/0x80
> Pid: 28022, comm: kio_thumbnail Not tainted 2.6.31-rc7 #1
> Call Trace:
> [<ffffffff810afaf4>] ? print_bad_pte+0x1d4/0x2c0
> [<ffffffff810afc79>] ? vm_normal_page+0x99/0xa0
> [<ffffffff810b0c7d>] ? unmap_vmas+0x4cd/0x970
> [<ffffffff810b6c74>] ? exit_mmap+0x104/0x1d0
> [<ffffffff81043e0d>] ? mmput+0x4d/0x100
> [<ffffffff81048d81>] ? exit_mm+0x101/0x150
> [<ffffffff8104b240>] ? do_exit+0x6c0/0x750
> [<ffffffff8104b326>] ? do_group_exit+0x56/0xd0
> [<ffffffff8104b3c2>] ? sys_exit_group+0x22/0x40
> [<ffffffff8100b7eb>] ? system_call_fastpath+0x16/0x1b
> Disabling lock debugging due to kernel taint
>
> No lockups or anything.

That looks like a memory corruption bug. Your page table entry is bad:
pte:ffff88006cc99128. It has the "special" bit set (one of the software
bits), in a mapping that should not have special pages.
But that pte entry is odd in other ways too - it's _PAGE_PROTNONE, which
is unusual (but not necessarily _wrong_) and _PAGE_BIT_ACCESSED. And it
has the high bits set, which is really not ok for a page table entry. The
PTE entry should look more like the pmd entry.

So it looks like the pte has been overwritten by some bogus value,
presumably by a stale pointer. And it migth be related to your inotify
problems that way.

Linus


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