Re: [PATCH v2 1/2] ceph/mdsc: Move CEPH_CAP_PIN reference when r_parent is updated

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On Thu, Sep 4, 2025 at 12:11 PM Alex Markuze <amarkuze@xxxxxxxxxx> wrote:
>
> When the parent directory lock is not held, req->r_parent can become stale and is updated to point to the correct inode.
> However, the associated CEPH_CAP_PIN reference was not being adjusted.
> The CEPH_CAP_PIN is a reference on an inode that is tracked for accounting purposes.
> Moving this pin is important to keep the accounting balanced. When the pin was not moved from the old parent to the new one, it created two problems:
> The reference on the old, stale parent was never released, causing a reference leak.
> A reference for the new parent was never acquired, creating the risk of a reference underflow later in ceph_mdsc_release_request().
> This patch corrects the logic by releasing the pin from the old parent and acquiring it for the new parent when r_parent is switched.
> This ensures reference accounting stays balanced.
>
> Signed-off-by: Alex Markuze <amarkuze@xxxxxxxxxx>
> Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@xxxxxxx>
> ---
>  fs/ceph/mds_client.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index ce0c129f4651..4e5926f36e8d 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -3053,12 +3053,19 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
>          */
>         if (!parent_locked && req->r_parent && path_info1.vino.ino &&
>             ceph_ino(req->r_parent) != path_info1.vino.ino) {
> +               struct inode *old_parent = req->r_parent;
>                 struct inode *correct_dir = ceph_get_inode(mdsc->fsc->sb, path_info1.vino, NULL);
>                 if (!IS_ERR(correct_dir)) {
>                         WARN_ONCE(1, "ceph: r_parent mismatch (had %llx wanted %llx) - updating\n",
> -                                 ceph_ino(req->r_parent), path_info1.vino.ino);
> -                       iput(req->r_parent);
> +                                 ceph_ino(old_parent), path_info1.vino.ino);
> +                       /*
> +                        * Transfer CEPH_CAP_PIN from the old parent to the new one.
> +                        * The pin was taken earlier in ceph_mdsc_submit_request().
> +                        */
> +                       ceph_put_cap_refs(ceph_inode(old_parent), CEPH_CAP_PIN);
> +                       iput(old_parent);
>                         req->r_parent = correct_dir;
> +                       ceph_get_cap_refs(ceph_inode(req->r_parent), CEPH_CAP_PIN);
>                 }
>         }
>
> --
> 2.34.1
>

Folded into "ceph: fix client race condition validating r_parent before
applying state" and queued up for 6.17-rc6.

Thanks,

                Ilya





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