Bug#901497: Reassigning to Xwayland

[Josh Triplett <josh@joshtriplett.org>]

reassign 901497
retitle 901497 Xwayland: hangs spinning on write and SIGALRM
thanks

After further investigation, I can reproduce this with Mesa 18.0.5-1 as
well, just not as often.

After encountering this issue, I managed to switch to a text console,
and found that Xwayland was using 100% CPU. strace of the running
Xwayland produced the attached strace, in which Xwayland appears to be
spinning, running a zero-byte writev, and periodically processing a
SIGALRM. Other threads appear to be blocked on futexes.

- Josh Triplett