[PATCH 05/11] lockdep: Remove softirq accounting on PREEMPT_RT.

Sebastian Andrzej Siewior
2021-11-29T22:31:50Z

From: Thomas Gleixner <tglx@linutronix.de>

There is not really a softirq context on PREEMPT_RT.
Softirqs on PREEMPT_RT are always invoked within the context of a
threaded interrupt handler or within ksoftirqd. The "in-softirq" context
is preemptible and is protected by a per-CPU lock to ensure mutual
exclusion.

There is no difference on PREEMPT_RT between spin_lock_irq() and
spin_lock() because the former does not disable interrupts. Therefore if
a lock is used in_softirq() and locked once with spin_lock_irq() then
lockdep will report this with "inconsistent {SOFTIRQ-ON-W} ->
{IN-SOFTIRQ-W} usage".

Teach lockdep that we don't really do softirqs on -RT.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/irqflags.h | 23 +++++++++++++++--------
kernel/locking/lockdep.c | 2 ++
2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 600c10da321a7..4b140938b03e2 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -71,14 +71,6 @@ do { \
do { \
__this_cpu_dec(hardirq_context); \
} while (0)
-# define lockdep_softirq_enter() \
-do { \
- current->softirq_context++; \
-} while (0)
-# define lockdep_softirq_exit() \
-do { \
- current->softirq_context--; \
-} while (0)

# define lockdep_hrtimer_enter(__hrtimer) \
({ \
@@ -140,6 +132,21 @@ do { \
# define lockdep_irq_work_exit(__work) do { } while (0)
#endif

+#if defined(CONFIG_TRACE_IRQFLAGS) && !defined(CONFIG_PREEMPT_RT)
+# define lockdep_softirq_enter() \
+do { \
+ current->softirq_context++; \
+} while (0)
+# define lockdep_softirq_exit() \
+do { \
+ current->softirq_context--; \
+} while (0)
+
+#else
+# define lockdep_softirq_enter() do { } while (0)
+# define lockdep_softirq_exit() do { } while (0)
+#endif
+
#if defined(CONFIG_IRQSOFF_TRACER) || \
defined(CONFIG_PREEMPT_TRACER)
extern void stop_critical_timings(void);
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2270ec68f10a1..4a882f83aeb9d 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5485,6 +5485,7 @@ static noinstr void check_flags(unsigned long flags)
}
}

+#ifndef CONFIG_PREEMPT_RT
/*
* We dont accurately track softirq state in e.g.
* hardirq contexts (such as on 4KSTACKS), so only
@@ -5499,6 +5500,7 @@ static noinstr void check_flags(unsigned long flags)
DEBUG_LOCKS_WARN_ON(!current->softirqs_enabled);
}
}
+#endif

if (!debug_locks)
print_irqtrace_events(current);
--
2.34.0