Found by the race detector and existing tests.
To avoid introducing a lock into this hot path,
calculate and cache whether any peers exist.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
The new test introduced in this commit used to deadlock about 1% of the time.
I believe that the deadlock occurs as follows:
* The test completes, calling device.Close.
* device.Close closes device.signals.stop.
* RoutineEncryption stops.
* The deferred function in RoutineEncryption drains device.queue.encryption.
* RoutineEncryption exits.
* A peer's RoutineNonce processes an element queued in peer.queue.nonce.
* RoutineNonce puts that element into the outbound and encryption queues.
* RoutineSequentialSender reads that elements from the outbound queue.
* It waits for that element to get Unlocked by RoutineEncryption.
* RoutineEncryption has already exited, so RoutineSequentialSender blocks forever.
* device.RemoveAllPeers calls peer.Stop on all peers.
* peer.Stop waits for peer.routines.stopping, which blocks forever.
Rather than attempt to add even more ordering to the already complex
centralized shutdown orchestration, this commit moves towards a
data-flow-oriented shutdown.
The device.queue.encryption gets closed when there will be no more writes to it.
All device.queue.encryption readers always read until the channel is closed and then exit.
We thus guarantee that any element that enters the encryption queue also exits it.
This removes the need for central control of the lifetime of RoutineEncryption,
removes the need to drain the encryption queue on shutdown, and simplifies RoutineEncryption.
This commit also fixes a data race. When RoutineSequentialSender
drains its queue on shutdown, it needs to lock the elem before operating on it,
just as the main body does.
The new test in this commit passed 50k iterations with the race detector enabled
and 150k iterations with the race detector disabled, with no failures.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
In each case, the starting waitgroup did nothing but ensure
that the goroutine has launched.
Nothing downstream depends on the order in which goroutines launch,
and if the Go runtime scheduler is so broken that goroutines
don't get launched reasonably promptly, we have much deeper problems.
Given all that, simplify the code.
Passed a race-enabled stress test 25,000 times without failure.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
Peers are currently removed after Device's goroutines are signaled to stop,
but without waiting for them to actually do so, which is racy.
For example, RoutineHandshake may be in Peer.SendKeepalive
when the corresponding peer is removed, which closes its nonce channel.
This causes a send on a closed channel, as observed in tailscale/tailscale#487.
This patch seems to be the correct synchronizing action:
Peer's goroutines are receivers and handle channel closure gracefully,
so Device's goroutines are the ones that should be fully stopped first.
Signed-Off-By: Dmytro Shynkevych <dmytro@tailscale.com>
The sticky socket code stays in the device package for now,
as it reaches deeply into the peer list.
This is the first step in an effort to split some code out of
the very busy device package.
Signed-off-by: David Crawshaw <crawshaw@tailscale.com>
