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    SubjectRe: Problem in log_do_checkpoint()?

    > On Mon, 2005-04-04 at 10:04, Jan Kara wrote:
    > > In log_do_checkpoint() we go through the t_checkpoint_list of a
    > > transaction and call __flush_buffer() on each buffer. Suppose there is
    > > just one buffer on the list and it is dirty. __flush_buffer() sees it and
    > > puts it to an array of buffers for flushing. Then the loop finishes,
    > > retry=0, drop_count=0, batch_count=1. So __flush_batch() is called - we
    > > drop all locks and sleep. While we are sleeping somebody else comes and
    > > makes the buffer dirty again (OK, that is not probable, but I think it
    > > could be possible).
    > Yes, there's no reason why not at that point.
    > > Now we wake up and call __cleanup_transaction().
    > > It's not able to do anything and returns 0.
    > I think the _right_ answer here is to have two separate checkpoint
    > lists: the current one, plus one for which the checkpoint write has
    > already been submitted. That way, we can wait for IO completion on
    > submitted writes without (a) getting conned into doing multiple rewrites
    > if there's somebody else dirtying the buffer; or (b) getting confused
    > about how much progress we're making. Buffers on the pre-write list get
    > written; buffers on the post-write list get waited for; and both count
    > as progress (eliminating the false assert-failure when we failed to
    > detect progress).
    Yes, this seems to be a better long-term solution. A hotfix (retrying
    after __flush_batch()) is attached if somebody is interested - it should
    be safe and is lightly tested.

    > The prevention of multiple writes in this case should also improve
    > performance a little.
    > That ought to be pretty straightforward, I think. The existing cases
    > where we remove buffers from a checkpoint shouldn't have to care about
    > which list_head we're removing from; those cases already handle buffers
    > in both states. It's only when doing the flush/wait that we have to
    > distinguish the two.
    Yes, AFAICS the changes should remain local to the checkpointing code
    (plus __unlink_buffer()). Should I write the patch or will you?

    Jan Kara <>
    SuSE CR Labs
    Fix possible false assertion failure in JBD checkpointing code.

    Signed-off-by: Jan Kara <>

    diff -rupX /home/jack/.kerndiffexclude linux-2.6.12-rc2/fs/jbd/checkpoint.c linux-2.6.12-rc2-checkpoint/fs/jbd/checkpoint.c
    --- linux-2.6.12-rc2/fs/jbd/checkpoint.c 2005-03-03 18:58:29.000000000 +0100
    +++ linux-2.6.12-rc2-checkpoint/fs/jbd/checkpoint.c 2005-04-05 13:26:42.000000000 +0200
    @@ -339,8 +339,10 @@ int log_do_checkpoint(journal_t *journal
    } while (jh != last_jh && !retry);

    - if (batch_count)
    + if (batch_count) {
    __flush_batch(journal, bhs, &batch_count);
    + retry = 1;
    + }

    * If someone cleaned up this transaction while we slept, we're
     \ /
      Last update: 2005-04-11 13:40    [W:0.026 / U:33.472 seconds]
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