[RFC/SRU Bionic 0/2] Reverts we probably want to do quickly

[Stefan Bader]

While we were looking for a regression I stumbled over two changes we
imported from 4.19.y in to Bionic. Both differ from the versions in
4.19.y and somehow I am suspicious that they might not be needed or even
might cause some harm.

The amdgpu change follows a change that is not in 4.15 where GEM objects
are stored in a different place and somehow I believe that this might
have added the need to release multiple references. Though I cannot find
the place where those multiple references are taken (which is the claim
of the fix). The test done before the release loop is using the same
reference as the modified fix code. So maybe it is ok. On the other hand
it is sometimes better not to change an apparently working system.

With the mutex change it was a missing removal of a __sched directive.
It was dropped from a function which appears to be the counterpart of a
new function that gets added with the fix. This function (which does
exist in 4.19 but not in 4.15 was added to 4.19 when adding Wound-Wait
mutexes:

commit 08295b3b5beec9aac0f7a9db86f0fc3792039da3
Author: Thomas Hellstrom <thellstrom at vmware.com>
Date:   Fri Jun 15 10:17:38 2018 +0200

    locking: Implement an algorithm choice for Wound-Wait mutexes
...
/*
+ * Add @waiter to a given location in the lock wait_list and set the
+ * FLAG_WAITERS flag if it's the first waiter.
+ */
+static void __sched
+__mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
+                  struct list_head *list)

The question is whether without this, the clearing is actually required
or potentially even be dangerous.

-Stefan

Stefan Bader (2):
  Revert "locking/mutex: clear MUTEX_FLAGS if wait_list is empty due to
    signal"
  Revert "drm/amd/amdgpu: fix refcount leak"

 drivers/gpu/drm/amd/amdgpu/amdgpu_fb.c |  3 ---
 kernel/locking/mutex-debug.c           |  4 ++--
 kernel/locking/mutex-debug.h           |  2 +-
 kernel/locking/mutex.c                 | 16 ++++------------
 kernel/locking/mutex.h                 |  4 +++-
 5 files changed, 10 insertions(+), 19 deletions(-)

-- 
2.25.1