linux-kernel - Re: [PATCH v2 0/5] seqlock: Introduce PREEMPT

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Message-ID: <20200915143028.GB2674@hirez.programming.kicks-ass.net>
Date:   Tue, 15 Sep 2020 16:30:28 +0200
From:   peterz@...radead.org
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Qian Cai <cai@...hat.com>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-next@...r.kernel.org, Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v2 0/5] seqlock: Introduce PREEMPT_RT support

On Tue, Sep 15, 2020 at 08:48:17PM +0800, Boqun Feng wrote:
> I think this happened because seqcount_##lockname##_init() is defined at
> function rather than macro, so when the seqcount_init() gets expand in

Bah! I hate all this :/

I suspect the below, while more verbose than I'd like is the best
option.

---
 include/linux/seqlock.h | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index f73c7eb68f27..76e44e6c0100 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -173,6 +173,19 @@ static inline void seqcount_lockdep_reader_access(const seqcount_t *s)
  * @lock:	Pointer to the associated lock
  */
 
+#define seqcount_LOCKNAME_init(s, _lock, lockname)			\
+	do {								\
+		seqcount_##lockname##_t *____s = (s);			\
+		seqcount_init(&____s->seqcount);			\
+		__SEQ_LOCK(____s->lock = (_lock));			\
+	} while (0)
+
+#define seqcount_raw_spinlock_init(s, lock)	seqcount_LOCKNAME_init(s, lock, raw_spinlock)
+#define seqcount_spinlock_init(s, lock)		seqcount_LOCKNAME_init(s, lock, spinlock)
+#define seqcount_rwlock_init(s, lock)		seqcount_LOCKNAME_init(s, lock, rwlock);
+#define seqcount_mutex_init(s, lock)		seqcount_LOCKNAME_init(s, lock, mutex);
+#define seqcount_ww_mutex_init(s, lock)		seqcount_LOCKNAME_init(s, lock, ww_mutex);
+
 /*
  * SEQCOUNT_LOCKNAME()	- Instantiate seqcount_LOCKNAME_t and helpers
  * seqprop_LOCKNAME_*()	- Property accessors for seqcount_LOCKNAME_t
@@ -190,13 +203,6 @@ typedef struct seqcount_##lockname {					\
 	__SEQ_LOCK(locktype	*lock);					\
 } seqcount_##lockname##_t;						\
 									\
-static __always_inline void						\
-seqcount_##lockname##_init(seqcount_##lockname##_t *s, locktype *lock)	\
-{									\
-	seqcount_init(&s->seqcount);					\
-	__SEQ_LOCK(s->lock = lock);					\
-}									\
-									\
 static __always_inline seqcount_t *					\
 __seqprop_##lockname##_ptr(seqcount_##lockname##_t *s)			\
 {									\
@@ -284,8 +290,8 @@ SEQCOUNT_LOCKNAME(ww_mutex,     struct ww_mutex, true,     &s->lock->base, ww_mu
 	__SEQ_LOCK(.lock	= (assoc_lock))				\
 }
 
-#define SEQCNT_SPINLOCK_ZERO(name, lock)	SEQCOUNT_LOCKNAME_ZERO(name, lock)
 #define SEQCNT_RAW_SPINLOCK_ZERO(name, lock)	SEQCOUNT_LOCKNAME_ZERO(name, lock)
+#define SEQCNT_SPINLOCK_ZERO(name, lock)	SEQCOUNT_LOCKNAME_ZERO(name, lock)
 #define SEQCNT_RWLOCK_ZERO(name, lock)		SEQCOUNT_LOCKNAME_ZERO(name, lock)
 #define SEQCNT_MUTEX_ZERO(name, lock)		SEQCOUNT_LOCKNAME_ZERO(name, lock)
 #define SEQCNT_WW_MUTEX_ZERO(name, lock) 	SEQCOUNT_LOCKNAME_ZERO(name, lock)