[PATCH 0/5] Re: [Intel-gfx] [BUG][REGRESSION] i915 gpu hangs under load

[Andrea Arcangeli]

I'm also getting kernel hangs every couple of days. For me it's still
not fixed here in 4.11-rc5. It's hard to reproduce, the best
reproducer is to build lineageos 14.1 on host while running LTP in a
guest to stress the guest VM.

Initially I thought it was related to the fact I upgraded the xf86
intel driver just a few weeks ago (I deferred any upgrade of the
userland intel driver since last July because of a regression that
never got fixed and broke xterm for me). After I found a workaround
for the userland regression (appended at the end for reference) I
started getting kernel hangs but they are separate issues as far as I
can tell.

It's not well tested so beware... (it survived a couple of builds and
some VM reclaim but that's it).

The first patch 1/5 is the potential fix for the i915 kernel hang. The
rest are incremental improvements.

And I've no great solution for when the shrinker was invoked with the
struct_mutex held and and recurse on the lock. I don't think we can
possibly wait in such case (other than flush work that the second
patch does) but then practically it shouldn't be a big deal, the big
RAM eater is unlikely to be i915 when the system is low on memory.

Andrea Arcangeli (5):
  i915: avoid kernel hang caused by synchronize rcu struct_mutex
    deadlock
  i915: flush gem obj freeing workqueues to add accuracy to the i915
    shrinker
  i915: initialize the free_list of the fencing atomic_helper
  i915: schedule while freeing the lists of gem objects
  i915: fence workqueue optimization

 drivers/gpu/drm/i915/i915_gem.c          | 15 +++++++++++++++
 drivers/gpu/drm/i915/i915_gem_shrinker.c | 15 +++++++++++----
 drivers/gpu/drm/i915/intel_display.c     |  7 ++++---
 3 files changed, 30 insertions(+), 7 deletions(-)

===
Userland workaround for unusable xterm after commit
3d3d18f086cdda72ee18a454db70ca72c6e3246c (unrelated to this kernel
issue, just for reference of what I'm running in userland).

diff --git a/src/sna/sna_accel.c b/src/sna/sna_accel.c
index 11beb90..d349203 100644
--- a/src/sna/sna_accel.c
+++ b/src/sna/sna_accel.c
@@ -17430,11 +17430,15 @@ sna_flush_callback(CallbackListPtr *list, pointer user_data, pointer call_data)
 {
 	struct sna *sna = user_data;
 
+#if 0
 	if (!sna->needs_dri_flush)
 		return;
+#endif
 
 	sna_accel_flush(sna);
+#if 0
 	sna->needs_dri_flush = false;
+#endif
 }
 
 static void