Re: [PATCH v2 2/2] ceph: quota: fix quota subdir mounts

["Yan, Zheng" <ukernel@gmail.com>]

On Tue, Mar 12, 2019 at 10:22 PM Luis Henriques <lhenriques@suse.com> wrote:
>
> The CephFS kernel client does not enforce quotas set in a directory that
> isn't visible from the mount point.  For example, given the path
> '/dir1/dir2', if quotas are set in 'dir1' and the filesystem is mounted with
>
>   mount -t ceph <server>:<port>:/dir1/ /mnt
>
> then the client won't be able to access 'dir1' inode, even if 'dir2' belongs
> to a quota realm that points to it.
>
> This patch fixes this issue by simply doing an MDS LOOKUPINO operation for
> unknown inodes.  Any inode reference obtained this way will be added to a
> list in ceph_mds_client, and will only be released when the filesystem is
> umounted.
>
> Link: https://tracker.ceph.com/issues/38482
> Reported-by: Hendrik Peyerl <hpeyerl@plusline.net>
> Signed-off-by: Luis Henriques <lhenriques@suse.com>
> ---
>  fs/ceph/mds_client.c |  15 ++++++
>  fs/ceph/mds_client.h |   2 +
>  fs/ceph/quota.c      | 106 +++++++++++++++++++++++++++++++++++++++----
>  fs/ceph/super.h      |   2 +
>  4 files changed, 115 insertions(+), 10 deletions(-)
>
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index 163fc74bf221..1dc24c3525fe 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -3656,6 +3656,8 @@ int ceph_mdsc_init(struct ceph_fs_client *fsc)
>         mdsc->max_sessions = 0;
>         mdsc->stopping = 0;
>         atomic64_set(&mdsc->quotarealms_count, 0);
> +       INIT_LIST_HEAD(&mdsc->quotarealms_inodes_list);
> +       spin_lock_init(&mdsc->quotarealms_inodes_lock);
>         mdsc->last_snap_seq = 0;
>         init_rwsem(&mdsc->snap_rwsem);
>         mdsc->snap_realms = RB_ROOT;
> @@ -3726,6 +3728,8 @@ static void wait_requests(struct ceph_mds_client *mdsc)
>   */
>  void ceph_mdsc_pre_umount(struct ceph_mds_client *mdsc)
>  {
> +       struct ceph_inode_info *ci;
> +
>         dout("pre_umount\n");
>         mdsc->stopping = 1;
>
> @@ -3738,6 +3742,17 @@ void ceph_mdsc_pre_umount(struct ceph_mds_client *mdsc)
>          * their inode/dcache refs
>          */
>         ceph_msgr_flush();
> +       /*
> +        * It's now safe to clean quotarealms_inode_list without holding
> +        * mdsc->quotarealms_inodes_lock
> +        */
> +       while (!list_empty(&mdsc->quotarealms_inodes_list)) {
> +               ci = list_first_entry(&mdsc->quotarealms_inodes_list,
> +                                     struct ceph_inode_info,
> +                                     i_quotarealms_inode_item);
> +               list_del(&ci->i_quotarealms_inode_item);
> +               iput(&ci->vfs_inode);
> +       }
>  }
>
>  /*
> diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
> index 729da155ebf0..58968fb338ec 100644
> --- a/fs/ceph/mds_client.h
> +++ b/fs/ceph/mds_client.h
> @@ -329,6 +329,8 @@ struct ceph_mds_client {
>         int                     stopping;      /* true if shutting down */
>
>         atomic64_t              quotarealms_count; /* # realms with quota */
> +       struct list_head        quotarealms_inodes_list;
> +       spinlock_t              quotarealms_inodes_lock;
>
>         /*
>          * snap_rwsem will cover cap linkage into snaprealms, and
> diff --git a/fs/ceph/quota.c b/fs/ceph/quota.c
> index 9455d3aef0c3..d1ab1b331c0d 100644
> --- a/fs/ceph/quota.c
> +++ b/fs/ceph/quota.c
> @@ -22,7 +22,16 @@ void ceph_adjust_quota_realms_count(struct inode *inode, bool inc)
>  static inline bool ceph_has_realms_with_quotas(struct inode *inode)
>  {
>         struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
> -       return atomic64_read(&mdsc->quotarealms_count) > 0;
> +       struct super_block *sb = mdsc->fsc->sb;
> +
> +       if (atomic64_read(&mdsc->quotarealms_count) > 0)
> +               return true;
> +       /* if root is the real CephFS root, we don't have quota realms */
> +       if (sb->s_root->d_inode &&
> +           (sb->s_root->d_inode->i_ino == CEPH_INO_ROOT))
> +               return false;
> +       /* otherwise, we can't know for sure */
> +       return true;
>  }
>
>  void ceph_handle_quota(struct ceph_mds_client *mdsc,
> @@ -68,6 +77,37 @@ void ceph_handle_quota(struct ceph_mds_client *mdsc,
>         iput(inode);
>  }
>
> +/*
> + * This function will try to lookup a realm inode.  If the inode is found
> + * (through an MDS LOOKUPINO operation), the realm->inode will be updated and
> + * the inode will also be added to an mdsc list which will be freed only when
> + * the filesystem is umounted.
> + */
> +static struct inode *lookup_quotarealm_inode(struct ceph_mds_client *mdsc,
> +                                            struct super_block *sb,
> +                                            struct ceph_snap_realm *realm)
> +{
> +       struct inode *in;
> +
> +       in = ceph_lookup_inode(sb, realm->ino);
> +       if (IS_ERR(in)) {
> +               pr_warn("Can't lookup inode %llx (err: %ld)\n",
> +                       realm->ino, PTR_ERR(in));
> +               return in;
> +       }
> +
> +       spin_lock(&mdsc->quotarealms_inodes_lock);
> +       list_add(&ceph_inode(in)->i_quotarealms_inode_item,
> +                &mdsc->quotarealms_inodes_list);
> +       spin_unlock(&mdsc->quotarealms_inodes_lock);
> +
> +       spin_lock(&realm->inodes_with_caps_lock);
> +       realm->inode = in;
> +       spin_unlock(&realm->inodes_with_caps_lock);
> +
> +       return in;
> +}
> +
>  /*
>   * This function walks through the snaprealm for an inode and returns the
>   * ceph_snap_realm for the first snaprealm that has quotas set (either max_files
> @@ -76,9 +116,15 @@ void ceph_handle_quota(struct ceph_mds_client *mdsc,
>   *
>   * Note that the caller is responsible for calling ceph_put_snap_realm() on the
>   * returned realm.
> + *
> + * Callers of this function need to hold mdsc->snap_rwsem.  However, if there's
> + * a need to do an inode lookup, this rwsem will be temporarily dropped.  Hence
> + * the 'retry' argument: if rwsem needs to be dropped and 'retry' is 'false'
> + * this function will return -EAGAIN; otherwise, the snaprealms walk-through
> + * will be restarted.
>   */
>  static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
> -                                              struct inode *inode)
> +                                              struct inode *inode, bool retry)
>  {
>         struct ceph_inode_info *ci = NULL;
>         struct ceph_snap_realm *realm, *next;
> @@ -88,6 +134,7 @@ static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
>         if (ceph_snap(inode) != CEPH_NOSNAP)
>                 return NULL;
>
> +restart:
>         realm = ceph_inode(inode)->i_snap_realm;
>         if (realm)
>                 ceph_get_snap_realm(mdsc, realm);
> @@ -95,11 +142,25 @@ static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
>                 pr_err_ratelimited("get_quota_realm: ino (%llx.%llx) "
>                                    "null i_snap_realm\n", ceph_vinop(inode));
>         while (realm) {
> +               bool has_inode;
> +
>                 spin_lock(&realm->inodes_with_caps_lock);
> -               in = realm->inode ? igrab(realm->inode) : NULL;
> +               has_inode = realm->inode;
> +               in = has_inode ? igrab(realm->inode) : NULL;
>                 spin_unlock(&realm->inodes_with_caps_lock);
> -               if (!in)
> +               if (has_inode && !in)
>                         break;
> +               if (!in) {
> +                       up_read(&mdsc->snap_rwsem);
> +                       in = lookup_quotarealm_inode(mdsc, inode->i_sb, realm);
> +                       down_read(&mdsc->snap_rwsem);
> +                       if (IS_ERR(in))
> +                               break;
> +                       ceph_put_snap_realm(mdsc, realm);
> +                       if (!retry)
> +                               return ERR_PTR(-EAGAIN);
> +                       goto restart;
> +               }
>
>                 ci = ceph_inode(in);
>                 has_quota = __ceph_has_any_quota(ci);
> @@ -125,9 +186,22 @@ bool ceph_quota_is_same_realm(struct inode *old, struct inode *new)
>         struct ceph_snap_realm *old_realm, *new_realm;
>         bool is_same;
>
> +restart:
> +       /*
> +        * We need to lookup 2 quota realms atomically, i.e. with snap_rwsem.
> +        * However, get_quota_realm may drop it temporarily.  By setting the
> +        * 'retry' parameter to 'false', we'll get -EAGAIN if the rwsem was
> +        * dropped and we can then restart the whole operation.
> +        */
>         down_read(&mdsc->snap_rwsem);
> -       old_realm = get_quota_realm(mdsc, old);
> -       new_realm = get_quota_realm(mdsc, new);
> +       old_realm = get_quota_realm(mdsc, old, true);
> +       new_realm = get_quota_realm(mdsc, new, false);
> +       if (PTR_ERR(new_realm) == -EAGAIN) {
> +               up_read(&mdsc->snap_rwsem);
> +               if (old_realm)
> +                       ceph_put_snap_realm(mdsc, old_realm);
> +               goto restart;
> +       }
>         is_same = (old_realm == new_realm);
>         up_read(&mdsc->snap_rwsem);
>
> @@ -166,6 +240,7 @@ static bool check_quota_exceeded(struct inode *inode, enum quota_check_op op,
>                 return false;
>
>         down_read(&mdsc->snap_rwsem);
> +restart:
>         realm = ceph_inode(inode)->i_snap_realm;
>         if (realm)
>                 ceph_get_snap_realm(mdsc, realm);
> @@ -173,12 +248,23 @@ static bool check_quota_exceeded(struct inode *inode, enum quota_check_op op,
>                 pr_err_ratelimited("check_quota_exceeded: ino (%llx.%llx) "
>                                    "null i_snap_realm\n", ceph_vinop(inode));
>         while (realm) {
> +               bool has_inode;
> +
>                 spin_lock(&realm->inodes_with_caps_lock);
> -               in = realm->inode ? igrab(realm->inode) : NULL;
> +               has_inode = realm->inode;
> +               in = has_inode ? igrab(realm->inode) : NULL;
>                 spin_unlock(&realm->inodes_with_caps_lock);
> -               if (!in)
> +               if (has_inode && !in)
>                         break;
> -
> +               if (!in) {
> +                       up_read(&mdsc->snap_rwsem);
> +                       in = lookup_quotarealm_inode(mdsc, inode->i_sb, realm);
> +                       down_read(&mdsc->snap_rwsem);
> +                       if (IS_ERR(in))
> +                               break;
> +                       ceph_put_snap_realm(mdsc, realm);
> +                       goto restart;
> +               }
>                 ci = ceph_inode(in);
>                 spin_lock(&ci->i_ceph_lock);
>                 if (op == QUOTA_CHECK_MAX_FILES_OP) {
> @@ -314,7 +400,7 @@ bool ceph_quota_update_statfs(struct ceph_fs_client *fsc, struct kstatfs *buf)
>         bool is_updated = false;
>
>         down_read(&mdsc->snap_rwsem);
> -       realm = get_quota_realm(mdsc, d_inode(fsc->sb->s_root));
> +       realm = get_quota_realm(mdsc, d_inode(fsc->sb->s_root), true);
>         up_read(&mdsc->snap_rwsem);
>         if (!realm)
>                 return false;
> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> index ce51e98b08ec..cc7766aeb73b 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -375,6 +375,8 @@ struct ceph_inode_info {
>         struct list_head i_snap_realm_item;
>         struct list_head i_snap_flush_item;
>
> +       struct list_head i_quotarealms_inode_item;
> +
>         struct work_struct i_wb_work;  /* writeback work */
>         struct work_struct i_pg_inv_work;  /* page invalidation work */
>

After reading the code carefully. I feel a little uncomfortable with
the "lookup_ino" in get_quota_realm.  how about populating directories
above the 'mount subdir' during mounting (similar to cifs_get_root ).

Regards
Yan, Zheng