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    Subject[RFC][PATCH] set_page_buffer_dirty should skip unmapped buffers
    Hi Andrew,

    I have been running into following bug while running fsx
    tests on 1k (ext3) filesystem all the time.

    ----------- [cut here ] --------- [please bite here ] ---------
    Kernel BUG at fs/buffer.c:2791
    invalid opcode: 0000 [1] SMP

    Its complaining about BUG_ON(!buffer_mapped(bh)).

    It was hard to track it down, needed lots of debug - but here
    is the problem & fix. Since the fix is in __set_page_buffer_dirty()
    code - I am wondering how it would effect others :(

    With this fix fsx tests ran for more than 16 hours (and still

    Please let me know, what you think.


    Patch to fix: Kernel BUG at fs/buffer.c:2791
    on 1k (2k) filesystems while running fsx.

    journal_commit_transaction collects lots of dirty buffer from
    and does a single ll_rw_block() to write them out. ll_rw_block()
    locks the buffer and checks to see if they are dirty and submits
    them for IO.

    In the mean while, journal_unmap_buffers() as part of
    truncate can unmap the buffer and throw it away. Since its
    a 1k (2k) filesystem - each page (4k) will have more than
    one buffer_head attached to the page and and we can't free
    up buffer_heads attached to the page (if we are not
    invalidating the whole page).

    Now, any call to set_page_dirty() (like msync_interval)
    could end up setting all the buffer heads attached to
    this page again dirty, including the ones those got
    cleaned up :(

    If ll_rw_block() runs now and sees the dirty bit it does
    submit_bh() on those buffer_heads and triggers the assert.

    Fix is to check if the buffer is mapped before setting its
    dirty bit in __set_page_dirty_buffers().

    Signed-off-by: Badari Pulavarty <>
    fs/buffer.c | 8 +++++++-
    1 file changed, 7 insertions(+), 1 deletion(-)

    Index: linux-2.6.18-rc5/fs/buffer.c
    --- linux-2.6.18-rc5.orig/fs/buffer.c 2006-09-01 08:20:51.000000000 -0700
    +++ linux-2.6.18-rc5/fs/buffer.c 2006-09-01 08:41:01.000000000 -0700
    @@ -846,7 +846,13 @@ int __set_page_dirty_buffers(struct page
    struct buffer_head *bh = head;

    do {
    - set_buffer_dirty(bh);
    + /*
    + * Its possible that, not all buffers attached to
    + * this page are mapped (cleaned up by truncate).
    + * If so, skip them.
    + */
    + if (buffer_mapped(bh))
    + set_buffer_dirty(bh);
    bh = bh->b_this_page;
    } while (bh != head);

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      Last update: 2006-09-01 17:49    [W:0.023 / U:0.664 seconds]
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