Re: [PATCH v5 1/6] libceph: allow requests to return immediately on full conditions if caller wishes

[Jeff Layton <jlayton@redhat.com>]

On Tue, 2017-03-28 at 16:22 +0200, Ilya Dryomov wrote:
> On Sat, Feb 25, 2017 at 6:43 PM, Jeff Layton <jlayton@redhat.com> wrote:
> > Usually, when the osd map is flagged as full or the pool is at quota,
> > write requests just hang. This is not what we want for cephfs, where
> > it would be better to simply report -ENOSPC back to userland instead
> > of stalling.
> > 
> > If the caller knows that it will want an immediate error return instead
> > of blocking on a full or at-quota error condition then allow it to set a
> > flag to request that behavior.
> > 
> > Set that flag in ceph_osdc_new_request (since ceph.ko is the only caller),
> > and on any other write request from ceph.ko.
> > 
> > A later patch will deal with requests that were submitted before the new
> > map showing the full condition came in.
> > 
> > Signed-off-by: Jeff Layton <jlayton@redhat.com>
> > ---
> >  fs/ceph/addr.c                  | 1 +
> >  fs/ceph/file.c                  | 1 +
> >  include/linux/ceph/osd_client.h | 1 +
> >  net/ceph/osd_client.c           | 7 +++++++
> >  4 files changed, 10 insertions(+)
> > 
> > diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> > index 6ecb920602ed..4b9da6ee5c7f 100644
> > --- a/fs/ceph/addr.c
> > +++ b/fs/ceph/addr.c
> > @@ -1889,6 +1889,7 @@ static int __ceph_pool_perm_get(struct ceph_inode_info *ci,
> >         err = ceph_osdc_start_request(&fsc->client->osdc, rd_req, false);
> > 
> >         wr_req->r_mtime = ci->vfs_inode.i_mtime;
> > +       wr_req->r_abort_on_full = true;
> >         err2 = ceph_osdc_start_request(&fsc->client->osdc, wr_req, false);
> > 
> >         if (!err)
> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > index 5a7134ef13d3..9dad32d0ed0b 100644
> > --- a/fs/ceph/file.c
> > +++ b/fs/ceph/file.c
> > @@ -712,6 +712,7 @@ static void ceph_aio_retry_work(struct work_struct *work)
> >         req->r_callback = ceph_aio_complete_req;
> >         req->r_inode = inode;
> >         req->r_priv = aio_req;
> > +       req->r_abort_on_full = true;
> > 
> >         ret = ceph_osdc_start_request(req->r_osdc, req, false);
> >  out:
> > diff --git a/include/linux/ceph/osd_client.h b/include/linux/ceph/osd_client.h
> > index f2ce9cd5ede6..55dcff2455e0 100644
> > --- a/include/linux/ceph/osd_client.h
> > +++ b/include/linux/ceph/osd_client.h
> > @@ -169,6 +169,7 @@ struct ceph_osd_request {
> >         unsigned int            r_num_ops;
> > 
> >         int               r_result;
> > +       bool              r_abort_on_full; /* return ENOSPC when full */
> 
> Move this under "set by submitter", after r_linger?
> 
> > 
> >         struct ceph_osd_client *r_osdc;
> >         struct kref       r_kref;
> > diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
> > index 5c0938ddddf6..8fc0ccc7126f 100644
> > --- a/net/ceph/osd_client.c
> > +++ b/net/ceph/osd_client.c
> > @@ -49,6 +49,7 @@ static void link_linger(struct ceph_osd *osd,
> >                         struct ceph_osd_linger_request *lreq);
> >  static void unlink_linger(struct ceph_osd *osd,
> >                           struct ceph_osd_linger_request *lreq);
> > +static void complete_request(struct ceph_osd_request *req, int err);
> 
> Move this closer to __submit_request(), before send_map_check() forward
> declaration?
> 
> > 
> >  #if 1
> >  static inline bool rwsem_is_wrlocked(struct rw_semaphore *sem)
> > @@ -961,6 +962,7 @@ struct ceph_osd_request *ceph_osdc_new_request(struct ceph_osd_client *osdc,
> >                                        truncate_size, truncate_seq);
> >         }
> > 
> > +       req->r_abort_on_full = true;
> >         req->r_flags = flags;
> >         req->r_base_oloc.pool = layout->pool_id;
> >         req->r_base_oloc.pool_ns = ceph_try_get_string(layout->pool_ns);
> > @@ -1635,6 +1637,7 @@ static void __submit_request(struct ceph_osd_request *req, bool wrlocked)
> >         enum calc_target_result ct_res;
> >         bool need_send = false;
> 
> bool need_abort here instead of ret?  This is a filesystem specific
> hack, so it's always going to be ENOSPC.
> 

Fixing all of the above for the next iteration.

> >         bool promoted = false;
> > +       int ret = 0;
> > 
> >         WARN_ON(req->r_tid);
> >         dout("%s req %p wrlocked %d\n", __func__, req, wrlocked);
> > @@ -1669,6 +1672,8 @@ static void __submit_request(struct ceph_osd_request *req, bool wrlocked)
> >                 pr_warn_ratelimited("FULL or reached pool quota\n");
> >                 req->r_t.paused = true;
> >                 maybe_request_map(osdc);
> > +               if (req->r_abort_on_full)
> > +                       ret = -ENOSPC;
> >         } else if (!osd_homeless(osd)) {
> >                 need_send = true;
> >         } else {
> > @@ -1685,6 +1690,8 @@ static void __submit_request(struct ceph_osd_request *req, bool wrlocked)
> >         link_request(osd, req);
> >         if (need_send)
> >                 send_request(req);
> > +       else if (ret)
> > +               complete_request(req, ret);
> 
> I think this is the first complete_request() on the submit thread, so
> I'm a little worried about possible deadlocks and/or other weirdness.
> Did you look through all start/handle_reply sites in the filesystem?
> 

I did. That's not to say I didn't miss anything, but as far as I can
tell, we expect to call complete_request with the osd locked, and it is
at this point in the __submit_request codepath.

Thanks for the comments so far!
-- 
Jeff Layton <jlayton@redhat.com>