linux-kernel - [PATCH 3/5] seqlock: introduce seqprop

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Date:   Wed, 13 Sep 2023 17:50:00 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>
Cc:     Alexey Gladkov <legion@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/5] seqlock: introduce seqprop_lock/unlock

which can be used to take/release the corresponding lock.

Thanks to the previous patch, it is trivial to pass 2 arguments to
the new __seqprop_##lockname##_lock/unlock "methods", plus we do not
loose the type info and thus the new seqprop's are "type safe".

So for example

	void func(seqcount_rwlock_t *s, rwlock_t *l)
	{
		seqprop_lock(s, l);
	}

happily compiles, but this one

	void func(seqcount_rwlock_t *s, spinlock_t *l)
	{
		seqprop_lock(s, l);
	}

doesn't.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 include/linux/seqlock.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 41e36f8afad4..9831683a0102 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -241,6 +241,21 @@ static __always_inline void						\
 __seqprop_##lockname##_assert(const seqcount_##lockname##_t *s)		\
 {									\
 	__SEQ_LOCK(lockdep_assert_held(s->lock));			\
+}									\
+									\
+static __always_inline void						\
+__seqprop_##lockname##_lock(seqcount_##lockname##_t *s,			\
+				locktype *lock)				\
+{									\
+	__SEQ_LOCK(WARN_ON_ONCE(s->lock != lock));			\
+	lockbase##_lock(lock);						\
+}									\
+									\
+static __always_inline void						\
+__seqprop_##lockname##_unlock(seqcount_##lockname##_t *s,		\
+				locktype *lock)				\
+{									\
+	lockbase##_unlock(lock); 					\
 }
 
 /*
@@ -306,6 +321,12 @@ SEQCOUNT_LOCKNAME(mutex,        struct mutex,    true,     mutex)
 #define seqprop_preemptible(s)		__seqprop(s, preemptible)(s)
 #define seqprop_assert(s)		__seqprop(s, assert)(s)
 
+/* seqcount_t doesn't have these methods */
+static inline void __seqprop_lock   (seqcount_t *s, void *l) { BUILD_BUG(); }
+static inline void __seqprop_unlock (seqcount_t *s, void *l) { BUILD_BUG(); }
+#define seqprop_lock(s, l)		__seqprop(s, lock)(s, l)
+#define seqprop_unlock(s, l)		__seqprop(s, unlock)(s, l)
+
 /**
  * __read_seqcount_begin() - begin a seqcount_t read section w/o barrier
  * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
-- 
2.25.1.362.g51ebf55