[tip: locking/core] lockdep: Remove softirq accounting on PREEMPT_RT.

tip-bot2 for Thomas Gleixner
2021-12-06T15:29:36Z

The following commit has been merged into the locking/core branch of tip:

Commit-ID: 0c1d7a2c2d32fac7ff4a644724b2d52a64184645
Gitweb: https://git.kernel.org/tip/0c1d7a2c2d32fac7ff4a644724b2d52a64184645
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Mon, 29 Nov 2021 18:46:48 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Sat, 04 Dec 2021 10:56:23 +01:00

lockdep: Remove softirq accounting on PREEMPT_RT.

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211129174654.668506-6-bigeasy@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 600c10d..4b14093 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 2270ec6..4a882f8 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);