This series should hopefully fix the lockups that some users have been experiencing with swap events enabled.

commit 076c6a8de05219800dd922827a223b345cdbc193 (HEAD -> swap-event-fixes)
Author: Fredrik Höglund <fredrik@kde.org>
Date: Sun May 12 14:21:03 2019 +0200

Remove the assert() in Compositor::bufferSwapComplete()

commit d9765fdb51be90718190c6495de5c8a9aa400fc3
Author: Fredrik Höglund <fredrik@kde.org>
Date: Sun May 12 14:19:12 2019 +0200

Set m_bufferSwapPending to false in Compositor::finish()

Othewise we can end up waiting forever if compositing was suspended
while a swap event was pending.

commit da1b607722e6fff5290b1e6d4c73447b8ac5444e
Author: Fredrik Höglund <fredrik@kde.org>
Date: Sun May 12 14:17:36 2019 +0200

Don't call performCompositing() directly from bufferSwapComplete()

Start the composite timer instead, so we don't call performCompositing()
from the event handler.

I've been running kwin with these patches and swap events enabled for a couple of months without experiencing any lockups.

Keep in mind that swap events must be enabled by setting KWIN_USE_INTEL_SWAP_EVENT to 1 when testing these changes.