[PATCH v9 0/7] Centralize and unify usage of preempt/irq

From: Joel Fernandes
Date: Thu Jun 07 2018 - 16:38:56 EST


From: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>

This is the next (hopefully close to final) revision of preempt/irq tracepoint
centralization and unified usage across the kernel. This revision mostly has
minor style corrections, reviewed-by tag additions and an improvement to the
test module. All patches now have a Reviewed-by tag except for the kselftest
script (patch 7/7). I have also now split out the softirq fix which really
should go into an -rc cycle and is independent of this series (see [1]).

The preempt/irq tracepoints exist but not everything in the kernel is using it
whenever they need to be notified that a preempt disable/enable or an irq
disable enable has occurred. This makes things not work simultaneously (for
example, only either lockdep or irqsoff trace-events can be used at a time).

This is particular painful to deal with, since turning on lockdep breaks
tracers that install probes on IRQ events, such as the BCC atomic critical
section tracer [2]. This constraint also makes it not possible to use synthetic
events to trace irqsoff sections with lockdep simulataneously turned on.

This series solves that, and also results in a nice clean up of relevant parts
of the kernel. Several ifdefs are simpler, and the design is more unified and
better. Also as a result of this, we also speeded performance all rcuidle
tracepoints since their handling is simpler.

[1] https://lkml.org/lkml/2018/6/7/1135
[2] https://github.com/iovisor/bcc/pull/1801/

v8->v9:
- Small style changes to tracepoint code (Mathieu)
- Minor style fix to use PTR_ERR_OR_ZERO (0-day bot)
- Minor fix to test_atomic_sections to use unsigned long.
- Added Namhyung's, Mathieu's Reviewed-by to some patches.

v7->v8:
- Refactored irqsoff tracer probe defines (Namhyung)

v6->v7:
- Added a module to simulate an atomic section, a kselftest to load and
and trigger it which verifies the preempt-tracer and this series.

- Fixed a new warning after I rebased in early boot, this is because
early_boot_irqs_disabled was set too early, I moved it after the lockdep
initialization.

- added back the softirq fix since it appears it wasn't picked up.

- Ran Ingo's locking API selftest suite which are passing with this
series.

- Mathieu suggested ifdef'ing the tracepoint_synchronize_unregister
function incase tracepoints aren't enabled, did that.

Joel Fernandes (Google) (6):
srcu: Add notrace variant of srcu_dereference
trace/irqsoff: Split reset into separate functions
tracepoint: Make rcuidle tracepoint callers use SRCU
tracing: Centralize preemptirq tracepoints and unify their usage
lib: Add module to simulate atomic sections for testing preemptoff
tracers
kselftests: Add tests for the preemptoff and irqsoff tracers

Paul McKenney (1):
srcu: Add notrace variants of srcu_read_{lock,unlock}

include/linux/ftrace.h | 11 +-
include/linux/irqflags.h | 11 +-
include/linux/lockdep.h | 8 +-
include/linux/preempt.h | 2 +-
include/linux/srcu.h | 22 ++
include/linux/tracepoint.h | 49 +++-
include/trace/events/preemptirq.h | 23 +-
init/main.c | 5 +-
kernel/locking/lockdep.c | 35 +--
kernel/sched/core.c | 2 +-
kernel/trace/Kconfig | 22 +-
kernel/trace/Makefile | 2 +-
kernel/trace/trace_irqsoff.c | 253 ++++++------------
kernel/trace/trace_preemptirq.c | 71 +++++
kernel/tracepoint.c | 16 +-
lib/Kconfig.debug | 8 +
lib/Makefile | 1 +
lib/test_atomic_sections.c | 77 ++++++
tools/testing/selftests/ftrace/config | 3 +
.../test.d/preemptirq/irqsoff_tracer.tc | 74 +++++
20 files changed, 454 insertions(+), 241 deletions(-)
create mode 100644 kernel/trace/trace_preemptirq.c
create mode 100644 lib/test_atomic_sections.c
create mode 100644 tools/testing/selftests/ftrace/test.d/preemptirq/irqsoff_tracer.tc

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2.17.1.1185.g55be947832-goog