git: DragonFly_RELEASE_4_0 drm: Use lockmgr locks with Linux wait queues
ftigeot at crater.dragonflybsd.org
Tue Nov 18 15:07:23 PST 2014
Author: FranÃ§ois Tigeot <ftigeot at wolfpond.org>
Date: Tue Nov 18 22:18:03 2014 +0100
drm: Use lockmgr locks with Linux wait queues
* On Linux, it is possible to grab a second spinlock in an already
spinlock-protected code section.
* The wait_event() macro is used in such a situation in the i915 driver.
One of the event checks itself tries to grab a second lock. What's more,
this second lock is a lockmgr lock in the DragonFly kernel. This results
in the following situation:
* Unfortunately if the lockmgr lock can't be acquired, the thread is put
to sleep and a thread sleeping with a spinlock held leads to a general
system freeze or a kernel panic.
* For that reason, we can't use a spinlock in Linux wait queues. Change
the internal wait_queue_head_t lock to a lockmgr lock.
Thanks go to Imre VadÃ¡sz for spotting this horrible issue.
Summary of changes:
sys/dev/drm/i915/i915_gem.c | 8 ++++----
sys/dev/drm/include/linux/completion.h | 18 +++++++++---------
sys/dev/drm/include/linux/wait.h | 10 +++++-----
3 files changed, 18 insertions(+), 18 deletions(-)
DragonFly BSD source repository
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