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    SubjectRe: [Q] missing unused dentry in prune_dcache()?
    Date
    Vasily Averin <vvs@sw.ru> wrote:

    > # If prune_dcache finds a dentry that it cannot free, it leaves it where it
    > # is (at the tail of the list) and exits, on the assumption that some other
    > # thread will be removing that dentry soon.
    >
    > However as far as I see this comment is not correct: when we cannot take
    > s_umount rw_semaphore (for example because it was taken in do_remount) this
    > dentry is already extracted from dentry_unused list and we do not add it into
    > the list again.

    You would seem to be correct.

    > Therefore dentry will not be found by prune_dcache() and shrink_dcache_sb()
    > and will leave in memory very long time until the partition will be
    > unmounted.

    And here too:-/

    > Am I probably err?

    Unfortunately not. I wonder if remount should be getting a writelock on the
    s_umount sem, but I don't see why not. grab_super() also gets a writelock on
    it, and so that could cause problems too.

    shrink_dcache_for_umount_subtree() doesn't care because it doesn't scan the
    dcache_unused list, but as you say, other things are affected.

    > The patch adds this dentry into tail of the dentry_unused list.

    I think that's reasonable. I wonder if we can avoid removing it from the list
    in the first place, but I suspect it's less optimal.

    Acked-By: David Howells <dhowells@redhat.com>
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