Commit 0c9794c8 authored by Ahmed S. Darwish's avatar Ahmed S. Darwish Committed by Peter Zijlstra
Browse files

seqlock: seqcount latch APIs: Only allow seqcount_latch_t 



All latch sequence counter call-sites have now been converted from plain
seqcount_t to the new seqcount_latch_t data type.

Enforce type-safety by modifying seqlock.h latch APIs to only accept
seqcount_latch_t.

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/20200827114044.11173-9-a.darwish@linutronix.de
parent 24bf401c

include/linux/seqlock.h

+15 −21
Original line number Diff line number Diff line
@@ -620,7 +620,7 @@ static inline void seqcount_latch_init(seqcount_latch_t *s) 


/**

 * raw_read_seqcount_latch() - pick even/odd latch data copy

 * @s: Pointer to seqcount_t, seqcount_raw_spinlock_t, or seqcount_latch_t

 * @s: Pointer to seqcount_latch_t

 *

 * See raw_write_seqcount_latch() for details and a full reader/writer

 * usage example.
@@ -629,17 +629,14 @@ static inline void seqcount_latch_init(seqcount_latch_t *s) 
 * picking which data copy to read. The full counter must then be checked

 * with read_seqcount_latch_retry().

 */

#define raw_read_seqcount_latch(s)						\

({										\

	/*									\

	 * Pairs with the first smp_wmb() in raw_write_seqcount_latch().	\

	 * Due to the dependent load, a full smp_rmb() is not needed.		\

	 */									\

	_Generic(*(s),								\

		 seqcount_t:		  READ_ONCE(((seqcount_t *)s)->sequence),			\

		 seqcount_raw_spinlock_t: READ_ONCE(((seqcount_raw_spinlock_t *)s)->seqcount.sequence),	\

		 seqcount_latch_t:	  READ_ONCE(((seqcount_latch_t *)s)->seqcount.sequence));	\

})

static inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s)

{

	/*

	 * Pairs with the first smp_wmb() in raw_write_seqcount_latch().

	 * Due to the dependent load, a full smp_rmb() is not needed.

	 */

	return READ_ONCE(s->seqcount.sequence);

}



/**

 * read_seqcount_latch_retry() - end a seqcount_latch_t read section
@@ -656,7 +653,7 @@ read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) 


/**

 * raw_write_seqcount_latch() - redirect latch readers to even/odd copy

 * @s: Pointer to seqcount_t, seqcount_raw_spinlock_t, or seqcount_latch_t

 * @s: Pointer to seqcount_latch_t

 *

 * The latch technique is a multiversion concurrency control method that allows

 * queries during non-atomic modifications. If you can guarantee queries never
@@ -735,14 +732,11 @@ read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) 
 *	When data is a dynamic data structure; one should use regular RCU

 *	patterns to manage the lifetimes of the objects within.

 */

#define raw_write_seqcount_latch(s)						\

{										\

       smp_wmb();      /* prior stores before incrementing "sequence" */	\

       _Generic(*(s),								\

		seqcount_t:		((seqcount_t *)s)->sequence++,		\

		seqcount_raw_spinlock_t:((seqcount_raw_spinlock_t *)s)->seqcount.sequence++, \

		seqcount_latch_t:	((seqcount_latch_t *)s)->seqcount.sequence++); \

       smp_wmb();      /* increment "sequence" before following stores */	\

static inline void raw_write_seqcount_latch(seqcount_latch_t *s)

{

	smp_wmb();	/* prior stores before incrementing "sequence" */

	s->seqcount.sequence++;

	smp_wmb();      /* increment "sequence" before following stores */

}



/*

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