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    SubjectRe: 2.6.18 ext3 panic.
    On Tue, 2006-10-10 at 17:03 -0500, Eric Sandeen wrote:
    > Jan Kara wrote:
    > > I think it's really the 1KB block size that makes it happen.
    > > I've looked at journal_dirty_data() code and I think the following can
    > > happen:
    > > sync() eventually ends up in journal_dirty_data(bh) as Eric writes.
    > > There is finds dirty buffer attached to the comitting transaction. So it drops
    > > all locks and calls sync_dirty_buffer(bh).
    > > Now in other process, file is truncated so that 'bh' gets just after EOF.
    > > As we have 1kb buffers, it can happen that bh is in the partially
    > > truncated page. Buffer is marked unmapped and clean. But in a moment the page
    > > is marked dirty and msync() is called. That eventually calls
    > > set_page_dirty() and all buffers in the page are marked dirty.
    > > The first process now wakes up, locks the buffer, clears the dirty bit
    > > and does submit_bh() - Oops.
    > Hm, just FWIW I have a couple traces* of the buffer getting unmapped
    > -before- journal_submit_data_buffers ever even finds it...
    > journal_submit_data_buffers():[fs/jbd/commit.c:242] needs writeout,
    > adding to array pid 1836
    > b_state:0x114025 b_jlist:BJ_SyncData cpu:0 b_count:2 b_blocknr:27130
    > b_jbd:1 b_frozen_data:0000000000000000
    > b_committed_data:0000000000000000
    > b_transaction:1 b_next_transaction:0 b_cp_transaction:0
    > b_trans_is_running:0
    > b_trans_is_comitting:1 b_jcount:0 pg_dirty:0
    > so it's already unmapped at this point. Could
    > journal_submit_data_buffers benefit from some buffer_mapped checks? Or
    > is that just a bandaid too late...


    b_state: 0x114025
    means BH_Mapped. Isn't it ?


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