Commit 52ac39e5 authored by Ahmed S. Darwish's avatar Ahmed S. Darwish Committed by Peter Zijlstra
Browse files

seqlock: seqcount_t: Implement all read APIs as statement expressions 



The sequence counters read APIs are implemented as CPP macros, so they
can take either seqcount_t or any of the seqcount_LOCKNAME_t variants.
Such macros then get *directly* transformed to internal C functions that
only take plain seqcount_t.

Further commits need access to seqcount_LOCKNAME_t inside of the actual
read APIs code. Thus transform all of the seqcount read APIs to pure GCC
statement expressions instead.

This will not break type-safety: all of the transformed APIs resolve to
a _Generic() selection that does not have a "default" case.

This will also not affect the transformed APIs readability: previously
added kernel-doc above all of seqlock.h functions makes the expectations
quite clear for call-site developers.

Signed-off-by: default avatarAhmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200904153231.11994-4-a.darwish@linutronix.de
parent 5cdd2557

include/linux/seqlock.h

+45 −49
Original line number Diff line number Diff line
@@ -184,6 +184,12 @@ __seqprop_##lockname##_ptr(seqcount_##lockname##_t *s) \ 
	return &s->seqcount;						\

}									\

									\

static __always_inline unsigned						\

__seqprop_##lockname##_sequence(const seqcount_##lockname##_t *s)	\

{									\

	return READ_ONCE(s->seqcount.sequence);				\

}									\

									\

static __always_inline bool						\

__seqprop_##lockname##_preemptible(const seqcount_##lockname##_t *s)	\

{									\
@@ -205,6 +211,11 @@ static inline seqcount_t *__seqprop_ptr(seqcount_t *s) 
	return s;

}



static inline unsigned __seqprop_sequence(const seqcount_t *s)

{

	return READ_ONCE(s->sequence);

}



static inline bool __seqprop_preemptible(const seqcount_t *s)

{

	return false;
@@ -250,6 +261,7 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base) 
	__seqprop_case((s),	ww_mutex,	prop))



#define __seqcount_ptr(s)		__seqprop(s, ptr)

#define __seqcount_sequence(s)		__seqprop(s, sequence)

#define __seqcount_lock_preemptible(s)	__seqprop(s, preemptible)

#define __seqcount_assert_lock_held(s)	__seqprop(s, assert)
@@ -268,21 +280,15 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base) 
 * Return: count to be passed to read_seqcount_retry()

 */

#define __read_seqcount_begin(s)					\

	__read_seqcount_t_begin(__seqcount_ptr(s))



static inline unsigned __read_seqcount_t_begin(const seqcount_t *s)

{

	unsigned ret;



repeat:

	ret = READ_ONCE(s->sequence);

	if (unlikely(ret & 1)) {

		cpu_relax();

		goto repeat;

	}

	kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);

	return ret;

}

({									\

	unsigned seq;							\

									\

	while ((seq = __seqcount_sequence(s)) & 1)			\

		cpu_relax();						\

									\

	kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);			\

	seq;								\

})



/**

 * raw_read_seqcount_begin() - begin a seqcount_t read section w/o lockdep
@@ -291,14 +297,12 @@ repeat: 
 * Return: count to be passed to read_seqcount_retry()

 */

#define raw_read_seqcount_begin(s)					\

	raw_read_seqcount_t_begin(__seqcount_ptr(s))



static inline unsigned raw_read_seqcount_t_begin(const seqcount_t *s)

{

	unsigned ret = __read_seqcount_t_begin(s);

	smp_rmb();

	return ret;

}

({									\

	unsigned seq = __read_seqcount_begin(s);			\

									\

	smp_rmb();							\

	seq;								\

})



/**

 * read_seqcount_begin() - begin a seqcount_t read critical section
@@ -307,13 +311,10 @@ static inline unsigned raw_read_seqcount_t_begin(const seqcount_t *s) 
 * Return: count to be passed to read_seqcount_retry()

 */

#define read_seqcount_begin(s)						\

	read_seqcount_t_begin(__seqcount_ptr(s))



static inline unsigned read_seqcount_t_begin(const seqcount_t *s)

{

	seqcount_lockdep_reader_access(s);

	return raw_read_seqcount_t_begin(s);

}

({									\

	seqcount_lockdep_reader_access(__seqcount_ptr(s));		\

	raw_read_seqcount_begin(s);					\

})



/**

 * raw_read_seqcount() - read the raw seqcount_t counter value
@@ -327,15 +328,13 @@ static inline unsigned read_seqcount_t_begin(const seqcount_t *s) 
 * Return: count to be passed to read_seqcount_retry()

 */

#define raw_read_seqcount(s)						\

	raw_read_seqcount_t(__seqcount_ptr(s))



static inline unsigned raw_read_seqcount_t(const seqcount_t *s)

{

	unsigned ret = READ_ONCE(s->sequence);

	smp_rmb();

	kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);

	return ret;

}

({									\

	unsigned seq = __seqcount_sequence(s);				\

									\

	smp_rmb();							\

	kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);			\

	seq;								\

})



/**

 * raw_seqcount_begin() - begin a seqcount_t read critical section w/o
@@ -355,16 +354,13 @@ static inline unsigned raw_read_seqcount_t(const seqcount_t *s) 
 * Return: count to be passed to read_seqcount_retry()

 */

#define raw_seqcount_begin(s)						\

	raw_seqcount_t_begin(__seqcount_ptr(s))



static inline unsigned raw_seqcount_t_begin(const seqcount_t *s)

{

	/*

	 * If the counter is odd, let read_seqcount_retry() fail

	 * by decrementing the counter.

	 */

	return raw_read_seqcount_t(s) & ~1;

}

({									\

	/*								\

	 * If the counter is odd, let read_seqcount_retry() fail	\

	 * by decrementing the counter.					\

	 */								\

	raw_read_seqcount(s) & ~1;					\

})



/**

 * __read_seqcount_retry() - end a seqcount_t read section w/o barrier

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