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    SubjectRe: BUG in ext2


    On Sun, 6 Aug 2000, Andrew Morton wrote:

    > > > I'm getting a 100% reproducible assertion failure at balloc.c:558:
    > > >
    > > > * way it could happen, thus the BUG().
    > > > */
    > > > if (*prealloc_count)
    > > > BUG();
    > > > *prealloc_count = 0;
    > > > *prealloc_block = next_block;
    > > > /* Writer: end */
    > > >
    > > > This is happening when running mmap002. I've put a gdb backtrace up at
    > > > http://www.uow.edu.au/~andrewm/ext2.txt
    > >
    > > Unfortunately, the whole ext2 block allocation code was re-written
    > > recently by Al Viro for test6-pre1, and it looks like it has bugs (see
    > > also thread <test6-pre2 loop in ext2_get_block>)...
    >
    > I suspect this problem is a simple one. Replacing the BUG() with a
    > printk(*prealloc_count) reveals that it is non-zero about six times during an
    > mmap002 run. Values vary from 1 to 7. No problems observed from this
    > workaround.

    Interesting... _If_ that happens - we have a bug somewhere that gives us a
    slow block leak.

    Look: if *prealloc_count is non-zero - we have several blocks (from
    *prealloc_block to *prealloc_block+*prealloc_count-1) marked as busy in
    the bitmap, but not attached to inode (yet). The next lines destroy all
    information about them - here's an instant leak for you. Normally
    ext2_discard_prealloc() would take care about freeing them, but it is not
    going to find them...

    _If_ that assertion is triggered - too bad, it means that we just didn't
    notice that leak until now.


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