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    SubjectRe: [lkp] [nfsd] b44061d0b9: BUG: Dentry ffff880027d7c540{i=1846f,n=0a} still in use (1) [unmount of btrfs vda]
    From
    Date
    On 08/10/2016 02:25 PM, Linus Torvalds wrote:
    > On Wed, Aug 10, 2016 at 11:22 AM, Josef Bacik <jbacik@fb.com> wrote:
    >> On 08/10/2016 02:06 PM, Linus Torvalds wrote:
    >>>
    >>> More information in the original email on lkml.
    >>
    >> I'm not subscribed to lkml and for some reason I can't find the original
    >> email in any of the lkml/linux-nfs archives. Could you forward more of the
    >> details?
    >
    > Done.
    >

    So my naive fix would be something like this


    From: Josef Bacik <jbacik@fb.com>
    Date: Wed, 10 Aug 2016 14:43:08 -0400
    Subject: [PATCH] nfsd: fix dentry refcounting problem

    b44061d0b9 introduced a dentry ref counting bug, previously we were grabbing one
    ref to dchild in nfsd_create(), but with the creation of nfsd_create_locked() we
    have a ref for dchild from the lookup in nfsd_create(), and then another ref in
    nfsd_create_locked(). The ref from the lookup in nfsd_create() is never dropped
    and results in dentries still in use at unmount.

    Signed-off-by: Josef Bacik <jbacik@fb.com>
    ---
    fs/nfsd/vfs.c | 9 ++++++---
    1 file changed, 6 insertions(+), 3 deletions(-)

    diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
    index ba944123..ff476e6 100644
    --- a/fs/nfsd/vfs.c
    +++ b/fs/nfsd/vfs.c
    @@ -1252,10 +1252,13 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
    if (IS_ERR(dchild))
    return nfserrno(host_err);
    err = fh_compose(resfhp, fhp->fh_export, dchild, fhp);
    - if (err) {
    - dput(dchild);
    + /*
    + * We unconditionally drop our ref to dchild as fh_compose will have
    + * already grabbed its own ref for it.
    + */
    + dput(dchild);
    + if (err)
    return err;
    - }
    return nfsd_create_locked(rqstp, fhp, fname, flen, iap, type,
    rdev, resfhp);
    }
    --
    2.5.5
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