sched: Prepare for per-cpu preempt_count
authorPeter Zijlstra <peterz@infradead.org>
Mon, 23 Sep 2013 17:04:26 +0000 (19:04 +0200)
committerIngo Molnar <mingo@kernel.org>
Wed, 25 Sep 2013 12:07:55 +0000 (14:07 +0200)
commita233f1120c37724938f7201fe2353b2577adaaf9
tree9d7b0887b3398a1fc699ea557822c891bf9c450d
parentbdb43806589096ac4272fe1307e789846ac08d7c
sched: Prepare for per-cpu preempt_count

When using per-cpu preempt_count variables we need to save/restore the
preempt_count on context switch (into per task storage; for instance
the old thread_info::preempt_count variable) because of
PREEMPT_ACTIVE.

However, this means that on fork() the preempt_count value of the last
context switch gets copied and if we had a PREEMPT_ACTIVE switch right
before cloning a child task the child task will now too have
PREEMPT_ACTIVE set and start its life with an extra PREEMPT_ACTIVE
count.

Therefore we need to make init_task_preempt_count() unconditional;
this resets whatever preempt_count we inherited from our parent
process.

Doing so for !per-cpu implementations is harmless.

For !PREEMPT_COUNT kernels we need to be careful not to start life
with an increased preempt_count.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-4k0b7oy1rcdyzochwiixuwi9@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
include/linux/sched.h
kernel/sched/core.c