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Date:   Sun, 24 May 2020 12:50:42 +0200
From:   "Sebastian A. Siewior" <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 07/25] lockdep: Add preemption disabled assertion API

On 2020-05-24 00:41:32 [+0200], Peter Zijlstra wrote:
> Because...? /me rummages around.. Ah you're proposing sticking this in
> seqcount itself and then header hell.
> 
> Moo.. ok I'll go have another look on Monday.

if you have a look on Monday you might want to start with the patch at
the bottom on top of the series. Both sched.h includes are needed also
you need to avoid write_seqcount_t_begin_nested() as static inline in
header files.

diff --git a/include/linux/flex_proportions.h b/include/linux/flex_proportions.h
index c12df59d3f5fc..c0f88f08371d7 100644
--- a/include/linux/flex_proportions.h
+++ b/include/linux/flex_proportions.h
@@ -12,6 +12,7 @@
 #include <linux/spinlock.h>
 #include <linux/seqlock.h>
 #include <linux/gfp.h>
+#include <linux/sched.h>
 
 /*
  * When maximum proportion of some event type is specified, this is the
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 54c929ea5b982..76385e599a9cb 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -702,13 +702,13 @@ do {									\
 			  "Not in hardirq as expected\n");		\
 	} while (0)
 
-/*
- * Don't define this assertion here to avoid a call-site's header file
- * dependency on sched.h task_struct current. This is needed by call
- * sites that are inline defined at header files already included by
- * sched.h.
- */
-void lockdep_assert_preemption_disabled(void);
+#define lockdep_assert_preemption_disabled() do {			\
+	WARN_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)      &&		\
+		  debug_locks                           &&		\
+		  !current->lockdep_recursion           &&		\
+		  (preempt_count() == 0 && current->hardirqs_enabled),	\
+		  "preemption not disabled as expected\n");		\
+       } while (0)
 
 #else
 # define might_lock(lock) do { } while (0)
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index eca464ecf012f..7f1261376110a 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -423,11 +423,11 @@ static inline void __write_seqcount_t_begin_nested(seqcount_t *s, int subclass)
 	seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_);
 }
 
-static inline void write_seqcount_t_begin_nested(seqcount_t *s, int subclass)
-{
-	lockdep_assert_preemption_disabled();
-	__write_seqcount_t_begin_nested(s, subclass);
-}
+#define write_seqcount_t_begin_nested(__s, __subclass)		\
+	do {							\
+		lockdep_assert_preemption_disabled();		\
+		__write_seqcount_t_begin_nested(__s, __subclass);\
+	} while (0)
 
 /*
  * write_seqcount_t_begin() without lockdep non-preemptibility check.
@@ -450,10 +450,7 @@ static inline void __write_seqcount_t_begin(seqcount_t *s)
  */
 #define write_seqcount_begin(s)		do_write_seqcount_begin(s)
 
-static inline void write_seqcount_t_begin(seqcount_t *s)
-{
-	write_seqcount_t_begin_nested(s, 0);
-}
+#define write_seqcount_t_begin(_s)	write_seqcount_t_begin_nested(_s, 0);
 
 /**
  * write_seqcount_end() - end a seqcount write-side critical section
diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h
index 30358ce3d8fe1..d0fd3edcdc50b 100644
--- a/include/linux/u64_stats_sync.h
+++ b/include/linux/u64_stats_sync.h
@@ -62,6 +62,7 @@
  * Example of use in drivers/net/loopback.c, using per_cpu containers,
  * in BH disabled context.
  */
+#include <linux/sched.h>
 #include <linux/seqlock.h>
 
 struct u64_stats_sync {
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 4dae65bc65c24..ac10db66cc63f 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5857,18 +5857,3 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
 	dump_stack();
 }
 EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);
-
-#ifdef CONFIG_PROVE_LOCKING
-
-void lockdep_assert_preemption_disabled(void)
-{
-	WARN_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&
-		  debug_locks				&&
-		  !current->lockdep_recursion		&&
-		  (preempt_count() == 0 && current->hardirqs_enabled),
-		  "preemption not disabled as expected\n");
-}
-EXPORT_SYMBOL_GPL(lockdep_assert_preemption_disabled);
-NOKPROBE_SYMBOL(lockdep_assert_preemption_disabled);
-
-#endif

Sebastian

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