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    SubjectRe: [BUG?] [Ext4] INFO: suspicious rcu_dereference_check() usage
    On Sun, Nov 21, 2010 at 08:30:24AM -0500, Ted Ts'o wrote:
    > On Sun, Nov 21, 2010 at 07:26:11PM +0800, Arun Bhanu wrote:
    > > I saw this in kernel log messages while testing 2.6.37-rc2. I think it
    > > appeared while mounting an external hard-disk. I can't seem to
    > > reproduce it.
    >
    > I could be wrong but this looks like it's a bug in mm/migrate.c in
    > migrate_page_move_mapping(): it is calling radix_tree_lookup_slot()
    > without first taking an rcu_read_lock().
    >
    > It was triggered by a memory allocation out of ext4_fill_super(),
    > which then triggered a memory compaction/migration, but I don't
    > believe it's otherwise related to the ext4 code.
    >
    > Over to the linux-mm folks for confirmation...

    I think it's no problem.

    That's because migration always holds lock_page on the file page.
    So the page couldn't remove from radix.


    --
    Kind regards,
    Minchan Kim


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