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From:   "Yan, Zheng" <ukernel@gmail.com>
Date:   Tue, 28 Apr 2020 21:41:55 +0800
Message-ID: <CAAM7YAnWM4oHgwBNXQWY5BOMDmZ9Pbqdd7N0DDedTO6HxQQeqg@mail.gmail.com>
Subject: Re: [PATCH] fs/ceph:fix double unlock in handle_cap_export()
To:     Wu Bo <wubo40@huawei.com>
Cc:     Jeff Layton <jlayton@kernel.org>, Sage Weil <sage@redhat.com>,
        Ilya Dryomov <idryomov@gmail.com>,
        ceph-devel <ceph-devel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        liuzhiqiang26@huawei.com, linfeilong@huawei.com
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On Tue, Apr 28, 2020 at 8:50 PM Wu Bo <wubo40@huawei.com> wrote:
>
> If the ceph_mdsc_open_export_target_session() return fails,
> should add a lock to avoid twice unlocking.
> Because the lock will be released at the retry or out_unlock tag.
>

at retry label, i_ceph_lock get locked. I don't see how i_ceph_lock
can get double unlock

> Signed-off-by: Wu Bo <wubo40@huawei.com>
> ---
>  fs/ceph/caps.c | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
> index 185db76..b5a62a8 100644
> --- a/fs/ceph/caps.c
> +++ b/fs/ceph/caps.c
> @@ -3731,22 +3731,24 @@ static void handle_cap_export(struct inode *inode, struct ceph_mds_caps *ex,
>
>         /* open target session */
>         tsession = ceph_mdsc_open_export_target_session(mdsc, target);
> -       if (!IS_ERR(tsession)) {
> -               if (mds > target) {
> -                       mutex_lock(&session->s_mutex);
> -                       mutex_lock_nested(&tsession->s_mutex,
> -                                         SINGLE_DEPTH_NESTING);
> -               } else {
> -                       mutex_lock(&tsession->s_mutex);
> -                       mutex_lock_nested(&session->s_mutex,
> -                                         SINGLE_DEPTH_NESTING);
> -               }
> -               new_cap = ceph_get_cap(mdsc, NULL);
> -       } else {
> +       if (IS_ERR(tsession)) {
>                 WARN_ON(1);
>                 tsession = NULL;
>                 target = -1;
> +               mutex_lock(&session->s_mutex);
> +               goto out_unlock;
> +       }
> +
> +       if (mds > target) {
> +               mutex_lock(&session->s_mutex);
> +               mutex_lock_nested(&tsession->s_mutex,
> +                                       SINGLE_DEPTH_NESTING);
> +       } else {
> +               mutex_lock(&tsession->s_mutex);
> +               mutex_lock_nested(&session->s_mutex,
> +                                       SINGLE_DEPTH_NESTING);
>         }
> +       new_cap = ceph_get_cap(mdsc, NULL);
>         goto retry;
>
>  out_unlock:
> --
> 1.8.3.1
>