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    SubjectRe: circular locking: /proc/sys/vm/drop_caches
    > On Fri, 23 Feb 2007 07:35:38 +0100 Ingo Molnar <mingo@elte.hu> wrote:
    > i just got the lockdep warning below when doing:
    >
    > echo 3 > /proc/sys/vm/drop_caches
    >
    > is this a known quirk in the drop_caches code?

    It is - we're taking inode_lock at just the wrong level there and I don't
    know how to fix it. The basic problem is that we're doing a list_head
    walk: if we drop the lock we have to start again.

    Well, I do know how to fix it: rip the various inode lists and use a tagged
    radix tree instead - make writeback's per-superblock inode walk work the
    same as writeback's per-inode page walk. That will also alow us to drop
    the lock and then resume the drop_caches thing at the point where we left
    off.

    But it's a large change and has some quite tricky issues which need to be
    carried over from the existing code and I don't have time to do it.

    The only (lame) thing I can say for now is that drop_caches is a
    debug-only, root-only thing :(

    -
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