[PATCH v2] Fix data races on hrtimer_sleeper ->task field

[Paul E. McKenney]

Hello!

In CONFIG_KCSAN_STRICT=y mode, KCSAN finds data races on the
hrtimer_sleeper structure's ->task field.  This field is used to indicate
owner of this structure, and also to signal the sleeper that the sleep
is over through use of a store of NULL.

Because access to the ->task field is open-coded across several kernel
subsystems, this series creates accessor functions creatively named
hrtimer_sleeper_task_get() and hrtimer_sleeper_task_set(), and uses
these throughout.

While in the area, also apply READ_ONCE() to lockless loads from
base->running.

A key goal of this and similar serieses is to reduce KCSAN noise in
strict mode so that new data races are more visible.

The series is as follows:

1.	Mark data-racy accesses to hrtimer_sleeper ->task field.

2.	Use accessor for hrtimer_sleeper ->task field.

3.	Use accessor for hrtimer_sleeper ->task field.

4.	Use accessor for hrtimer_sleeper ->task field.

5.	Use accessor for hrtimer_sleeper ->task field in waitwake.c.

6.	Use accessor for hrtimer_sleeper ->task field in sleep_timeout.c.

7.	pktgen: Use accessor for hrtimer_sleeper ->task field.

8.	Use accessor for hrtimer_sleeper ->task field.

9.	Use accessor for hrtimer_sleeper ->task field in requeue.

10.	Update hrtimer_resolution only if value changes.

11.	Mark the hrtimer_sleeper structure's ->task field __private.

12.	Apply READ_ONCE() to lockless base->running loads.

						Thanx, Paul

Changes since RFC v1:

o	Add patch 10 to avoid both cache misses and KCSAN false positives
	when updating hrtimer_resolution.

o	Add patch 11 to mark the hrtimer_sleeper structure's ->task
	field __private, as suggested by Thomas Gleixner.

o	Add patch 12 for a similar KCSAN issue involving lockless
	loads from base->running.

------------------------------------------------------------------------

 b/fs/aio.c                    |    2 +-
 b/include/linux/hrtimer.h     |    8 ++++++++
 b/include/linux/wait.h        |    2 +-
 b/io_uring/rw.c               |    2 +-
 b/kernel/futex/requeue.c      |    2 +-
 b/kernel/futex/waitwake.c     |    8 ++++----
 b/kernel/locking/rtmutex.c    |    2 +-
 b/kernel/time/hrtimer.c       |   14 +++++++-------
 b/kernel/time/sleep_timeout.c |    4 ++--
 b/net/core/pktgen.c           |    4 ++--
 include/linux/hrtimer.h       |    6 +++---
 kernel/time/hrtimer.c         |    9 +++++----
 12 files changed, 36 insertions(+), 27 deletions(-)