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    SubjectRe: [RFC][PATCH] ext3: don't read inode block if the buffer has a write error
    On Mon, 23 Jun 2008 21:46:27 +1000 Nick Piggin <> wrote:

    > On Monday 23 June 2008 21:25, Hidehiro Kawai wrote:
    > > A transient I/O error can corrupt inode data. Here is the scenario:
    > >
    > > (1) update inode_A at the block_B
    > > (2) pdflush writes out new inode_A to the filesystem, but it results
    > > in write I/O error, at this point, BH_Uptodate flag of the buffer
    > > for block_B is cleared and BH_Write_EIO is set
    > > (3) create new inode_C which located at block_B, and
    > > __ext3_get_inode_loc() tries to read on-disk block_B because the
    > > buffer is not uptodate
    > > (4) if it can read on-disk block_B successfully, inode_A is
    > > overwritten by old data
    > >
    > > This patch makes __ext3_get_inode_loc() not read the inode block if
    > > the buffer has BH_Write_EIO flag. In this case, the buffer should
    > > have the latest information, so setting the uptodate flag to the
    > > buffer (this avoids WARN_ON_ONCE() in mark_buffer_dirty().)
    > >
    > > According to this change, we would need to test BH_Write_EIO flag for
    > > the error checking. Currently nobody checks write I/O errors on
    > > metadata buffers, but it will be done in other patches I'm working on.
    > IMO there is a problem with all the buffer head and pagecache error
    > handling in that uptodate gets cleared on write errors. This is not
    > only wrong (because the in-memory copy continues to contain the most
    > uptodate copy), but it will trigger assertions all over the mm and
    > buffer code AFAIKS.
    > I don't know why it was done like this, or if anybody actually tested
    > any of it, but AFAIKS the best way to fix this is to simply not
    > clear any uptodate bits upon write errors.

    There's a plausible-sounding reason for this behaviour which I forgot
    about three years ago. Maybe Linus remembers?

    Meanwhile I guess I'll queue the patch, sad though it is.

     \ /
      Last update: 2008-06-24 04:21    [W:0.027 / U:2.288 seconds]
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