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

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 600c10d..4b14093 100644 (file)
--- 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 (file)
--- 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);