[PATCH v2 0/7] sched: Diagnostic checks for missing rq clock updates

From: Matt Fleming
Date: Wed Sep 21 2016 - 09:38:23 EST

There are currently no runtime diagnostic checks for detecting when we
have inadvertently missed a call to update_rq_clock() before accessing
rq_clock() or rq_clock_task().

The idea in these patches, which came from Peter, is to piggyback on
the rq->lock pin/unpin context to detect when we expected (and failed)
to see an update to the rq clock. They've already caught a couple of
bugs: see commit b52fad2db5d7 ("sched/fair: Update rq clock before
updating nohz CPU load").

All the diagnostic code is guarded by CONFIG_SCHED_DEBUG, but there
are minimal changes to __schedule() in patch 5 for the !SCHED_DEBUG

Jan and Sergey, Petr asked that you be Cc'd on this series because of
the recent issues with using WARN_ON() in the async printk work.

Changes in v2:

- Add a check for missing update_rq_clock() before rq_clock_task().

- Address review comments from Yuyang where I messed up the
__schedule() ::clock_update_flags manipulation

Matt Fleming (7):
sched/fair: Update the rq clock before detaching tasks
sched/fair: Update rq clock before waking up new task
sched/fair: Update rq clock in task_hot()
sched: Add wrappers for lockdep_(un)pin_lock()
sched/core: Reset RQCF_ACT_SKIP before unpinning rq->lock
sched/fair: Push rq lock pin/unpin into idle_balance()
sched/core: Add debug code to catch missing update_rq_clock()

kernel/sched/core.c | 92 +++++++++++++++++++++-------------------
kernel/sched/deadline.c | 10 ++---
kernel/sched/fair.c | 40 +++++++++++-------
kernel/sched/idle_task.c | 2 +-
kernel/sched/rt.c | 6 +--
kernel/sched/sched.h | 107 ++++++++++++++++++++++++++++++++++++++++-------
kernel/sched/stop_task.c | 2 +-
7 files changed, 177 insertions(+), 82 deletions(-)