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    SubjectRe: Bug in drivers/block/ll_rw_blk.c ?
      Hi Yoav!

    Yoav Weiss writes:
    > A few days ago I posted the report attached below. After some more
    > research, I'm starting to think I've hit a bug in ll_rw_blk.c.
    >
    > If the maintainer of the block dev subsystem happens to be reading
    > this, please contact me on the list or by mail.

    I'm not the maintainer, but I'm pretty sure that there is no problem in
    that specific code... but I think you're hitting another bug in the 2.4
    tree (read below...)

    [...snip...]

    > The cloop (compressed loop) code I'm debugging is this one:
    >
    > http://developer.linuxtag.net/knoppix/sources/cloop_1.0-2.tar.gz
    >
    > I'm testing with kernel 2.4.22-rc2.

    [...snip...]

    > The stalled process waits on a page in mm/filemap.c:1505:
    >
    > /* Again, try some read-ahead while waiting for the page to finish.. */
    > generic_file_readahead(reada_ok, filp, inode, page);
    > ------> wait_on_page(page);
    >
    >
    > I found who wakes it up in calls that don't stall:
    > unlock_page(), called from
    > drivers/block/ll_rw_blk.c:end_that_request_first().
    > bh->b_end_io(bh, uptodate) seems to do it.


    From this description it seems that you are hitting a bug which was
    discussed to death here on the list. Here's a thread with 143 messages for
    you:

    http://marc.theaimsgroup.com/?t=105400721000001&r=5&w=2

    And here are the threads in which a solution was dicussed:

    http://marc.theaimsgroup.com/?t=105519528200001&r=1&w=2
    http://marc.theaimsgroup.com/?t=105769525800005&r=3&w=2

    Notice, however, that the patch Chris, Andrea, Jens and others made for
    this problem is _already_ included in 2.4 (so, yes, 2.4.22-rc2 has the
    fix).

    So, you are probably hitting the same bug, which was not fixed 100%. If
    you think that your test is very easily reproducible and can shed more
    light on this problem, perhaps you should write to Chris, Andrea and Jens
    (with Cc: to the list), and show them the test. I don't know if they would
    be willing to spend more time on this issue, specially with 2.6 around the
    corner...

    best regards,

    --
    Livio B. Soares
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