[Mesa-dev] threads and X.org/AIGLX drivers

[Dave Airlie]

Hey,

So we got a bug reported against F15 where we were getting an illegal
input event type 0, after passing it around the RH X team I eventually
came to look at it.

The problem appears to be that we are using llvmpipe as our swrast
renderer and on systems that fallback to that we end up with threads
inside the X server, that we didn't spawn. It appears SIGIO gets
delivered to one of these threads while the main thread keeps on
trucking and fail ensues.

So I'm crossposting this as there are two fixes we can do that aren't
exclusive but could act as belt and braces on Linux at least (other
OSes get the belt only).

Fix 1: use F_SETOWN_EX, thank to DrNick and AaronP on irc for digging
up this nugget, "From  Linux  2.6.32 onwards, use F_SETOWN_EX to
target SIGIO
                and SIGURG signals at a particular thread.". So on
Linux we would use that instead of F_SETOWN to make sure SIGIO only
goes to the main X process/thread. Though I'm not sure how to get the
defintion for gettid which we need, though I'll look into this a bit
more.

Fix 2: block all signals in the gallium thread spawning code, this
involves using pthread_sigmask around the pthread_create function.
Calling it once with a full set of signals to block, and get a copy of
the current signals, then calling it again to put back the current
signals. I think this might be a good plan for some other things, as I
can't see a good reason for a DRI driver to ever get SIGIO, esp as it
may interfere with the parent app.

I've built a test package with 2 in it for Fedora and am awaiting
feedback from the tester, but just though I'd raise the subject here
for some discussion/feedback.

Dave.