OK, here's a weird one.. ;)

Dell Latitude D820 laptop, x86_64 kernel and userspace.

Symptom: The 'xmms' media player will consistently (every time) get stuck and
keep repeating the first 1 second or so of the song over and over (sounding
very similar to how an audio card will keep looping the ring buffer if the
system crashes). However, xmms is responsive.  It claims it's making progress
through the song - and the spectrum analyzer display is changing, *not* looping
the same second over and over.

The spectrum analyzer convinces me that the xmms thread reading from disk is
getting new data, but I'm unable to tell if the looping is happening on the
xmms->pulseaudio handoff or the pulseaudio->ALSA side.

Bisect results:

shmem-unify-regular-and-tiny-shmem.patch        GOOD
#
page_fault-retry-with-nopage_retry.patch
page_fault-retry-with-nopage_retry-fix.patch
page_fault-retry-with-nopage_retry-fix-fix.patch        BAD