Comment 2 for bug 155312

I have an strace of the event now. The whole strace is huge, but at one point this happens:

gettimeofday({1193220908, 897516}, NULL) = 0
gettimeofday({1193220908, 897569}, NULL) = 0
rt_sigprocmask(SIG_BLOCK, [IO], [], 8) = 0
--- SIGALRM (Alarm clock) @ 0 (0) ---
sigreturn() = ? (mask now [IO])
--- SIGALRM (Alarm clock) @ 0 (0) ---
sigreturn() = ? (mask now [IO])

Then the SIGALARM and sigreturn as above alternate with nothing inbetween them (about 20k times) until I kill X. Nowhere else does such a tight loop appear to occur in the strace log, so I reckon this is the point from which X gobbles 99% CPU and freezes.