objecter: don't resend paused ops

Paused ops are meant to block on the client side until a new map that
unpauses them is recieved. If we send paused writes when the FULL flag
is set, we'll get -ENOSPC from the osds, which is not what Objecter
users expect. This may cause rbd without caching to produce an I/O
error instead of waiting for the cluster to have capacity.

Fixes: #6725
Backport: dumpling
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
objecter: set op->paused in recalc_op_target(), resend in not paused

When going through scan_requests() in handle_osd_map() we need to make
sure that if an op should not be paused anymore then set it on the op
itself, and return NEED_RESEND. Otherwise we're going to miss reset of
the full flag.
Also in handle_osd_map(), make sure that op shouldn't be paused before
sending it. There's a lot of cleanup around that area that we should
probably be doing, make the code much more tight.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
objecter: clean pause / unpause logic

op->paused holds now whether operation should be paused or not, and it's
being updated when scanning requests. No need to do a second scan.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
osd: drop writes when full instead of returning an error

There's a race between the client and osd with a newly marked full
osdmap.  If the client gets the new map first, it blocks writes and
everything works as expected, with no errors from the osd.

If the osd gets the map first, however, it will respond to any writes
with -ENOSPC. Clients will pass this up the stack, and not retry these
writes later.  -ENOSPC isn't handled well by all clients. RBD, for
example, may pass it on to qemu or kernel rbd which will both
interpret it as EIO.  Filesystems on top of rbd will not behave well
when they receive EIOs like this, especially if the cluster oscillates
between full and not full, so some writes succeed.

To fix this, never return ENOSPC from the osd because of a map marked
full, and rely on the client to retry all writes when the map is no
longer marked full.

Old clients talking to osds with this fix will hang instead of
propagating an error, but only if they run into this race
condition. ceph-fuse and rbd with caching enabled are not affected,
since the ObjectCacher will retry writes that return errors.

Refs: #6938
Backport: dumpling, emperor
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
objecter: resend all writes after osdmap loses the full flag

Now that the osd does not respond if it gets a map with the full flag
set first, clients need to resend all writes.

Clients talking to old osds are still subject to the race condition,
so both sides must be upgraded to avoid it.

Refs: #6938
Backport: dumpling, emperor
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
rbd: check write return code during bench-write

This is allows rbd-bench to detect http://tracker.ceph.com/issues/6938
when combined with rapidly changing the mon osd full ratio.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
objecter: don't take extra throttle budget for resent ops

These ops have already taken their budget in the original op_submit().
It will be returned via put_op_budget() when they complete.
If there were many localized reads of missing objects from replicas,
or cache pool redirects, this would cause the objecter to use up all
of its op throttle budget and hang.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
Merge remote-tracking branch 'gh/wip-objecter-full-2'

Reviewed-by: Sage Weil <sage@inktank.com>