msg/Pipe: assert lock is held in various helpers

These all require that we hold pipe_lock.

Signed-off-by: Sage Weil <sage@inktank.com>
msg/Pipe: avoid creating empty out_q entry

We need to maintain the invariant that all sub queues in out_q are never
empty.  Fix discard_requeued_up_to() to avoid creating an entry unless we
know it is already present.

This bug leads to an incorrect reconnect attempt when

 - we accept a pipe (lossless peer)
 - they send some stuff, maybe
 - fault
 - we initiate reconnect, even tho we have nothing queued

In particular, we shouldn't reconnect because we aren't checking for
resets, and the fact that our out_seq is 0 while the peer's might be
something else entirely will trigger asserts later.

This fixes at least one source of #5626, and possibly #5517.

Backport: cuttlefish
Signed-off-by: Sage Weil <sage@inktank.com>
msg/Pipe: unlock msgr->lock earlier in accept()

Small cleanup.  Nothing needs msgr->lock for the previously larger
window.

Signed-off-by: Sage Weil <sage@inktank.com>
msgr: mark_down_all() during, not before, rebind

If we are shutting down all old connections and binding to new ports,
we want to avoid a sequence like:

 - close all prevoius connections
 - new connection comes in on old port
 - rebind to new ports
 -> connection from old port leaks through

As a first step, close all connections after we shut down the old
accepter and before we start the new one.

Signed-off-by: Sage Weil <sage@inktank.com>
msgr: maintain list of accepting pipes

New pipes exist in a sort of limbo before we know who the peer is and
add them to rank_pipe.  Keep a list of them in accepting_pipes for that
period.

Signed-off-by: Sage Weil <sage@inktank.com>
msgr: close accepting_pipes from mark_down_all()

We need to catch these pipes too, particularly when doing a rebind(),
to avoid them leaking through.

Signed-off-by: Sage Weil <sage@inktank.com>
msg/Pipe: hold pipe_lock during important parts of accept()

Previously we did not bother with locking for accept() because we were
not visible to any other threads.  However, we need to close accepting
Pipes from mark_down_all(), which means we need to handle interference.

Fix up the locking so that we hold pipe_lock when looking at Pipe state
and verify that we are still in the ACCEPTING state any time we retake
the lock.

Signed-off-by: Sage Weil <sage@inktank.com>
debug
debug osd mark_down