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    SubjectRe: [GIT PULL] Core block IO bits for 2.6.39 - early Oops
    On 2011-03-25 12:59, Theodore Tso wrote:
    >
    > On Mar 25, 2011, at 12:41 AM, Dave Chinner wrote:
    >
    >>>
    >>> It works insofar as the Oops is gone. But my xfs partitions apparently
    >>> still get corrupted (I had to run xfs_repair on several of them, because
    >>> they would not mount otherwise).
    >>
    >> So the patchset is causing repeatable filesystem corruption? Sounds
    >> to me like this series is not yet ready for mainline merging. Last
    >> thing I want to spend the .39 cycle helping people recover busted
    >> filesystems as a result of undercooked block layer changes...
    >
    > FYI. I did a trial merge last night of the ext4 changes last night with
    > the tip of Linus's tree. The ext4 changes (based on 2.6.38-rc5)
    > survived xfstests -g auto before I merged in Linus's 2.6.39 master
    > branch. After I merged with 2.6.39-tip, I reran xfstests, and it got
    > past test #13 (fsstress), which normally means that everything is
    > OK, so I sent a pull request to Linus. Much later, (-g auto takes a
    > long time) I got an OOPS inside the virtio driver. Ext4 was nowhere
    > in the stack trace, but of course the block layer was. Grumbling
    > that someone had broke virtio during the merge window, I switched
    > my KVM setup to use SATA emulation and used the sda devices
    > instead. This time I got an oops in the block I/O layer, again quite
    > late in xfstests. Somewhere around test #224 or so if I remember
    > correctly.
    >
    > It was too late last night to do any more investigating, which is why
    > I hadn't sent a formal report yet, but next up is for me to retry xfstests
    > before merging in my changes, and then to start a git bisect.
    >
    > So before accusing some patch series which hasn't been merged
    > into 2.6.39 yet, you might want to also worry about some change
    > that already has been merged. Of course the symptoms for me are
    > quite different. I'm not seeing an early oops, but only something
    > which shows up when the the system is put under a lot of stress
    > by xfstests. So it could be a different problem....
    >
    > - Ted
    >
    > P.S. And of course there is the chance that there is some
    > subtle bug in the ext4 branch, which worked just fine when
    > it was just based on 2.6.38-rc5, but which only manifested
    > itself when I merged in the tip of Linus's branch. So I'm not
    > __accusing__ the block layer yet, even though the stack traces
    > seem to point that way, because I don't have a smoking gun
    > yet. But I do have to admit I'm suspicious....

    But this plugging change is merged, so it is a very likely candidate.
    With the oddness going on, I suspect that we end up flushing a plug that
    resides on a stack that is no longer valid.

    Is there a way to check whether a given pointer is valid on the current
    stack for this process?

    I think we can rule out stack overflows, since the plug context itself
    is very small (28 bytes). But if we have something like:

    blk_start_plug(&plug1);
    ...
    blk_start_plug(&plug2);
    ...
    flush(&plug2);

    then that could explain the corruption and lockups.

    So I'd really like to have something ala:

    if (is_str_ptr_valid(current, ptr, size))
    ...

    to aid the debugging.

    --
    Jens Axboe



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