[PATCH 3/5] seqlock: introduce seqprop_lock/unlock

Oleg Nesterov
2023-09-13T15:51:51Z

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@redhat.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