[tip: locking/core] seqlock: seqcount latch APIs: Only allow seqcount_latch_t

tip-bot2 for Ahmed S. Darwish
2020-09-10T19:27:43Z

The following commit has been merged into the locking/core branch of tip:

Commit-ID: 0c9794c8b6781eb7dad8e19b78c5d4557790597a
Gitweb: https://git.kernel.org/tip/0c9794c8b6781eb7dad8e19b78c5d4557790597a
Author: Ahmed S. Darwish <a.darwish@linutronix.de>
AuthorDate: Thu, 27 Aug 2020 13:40:44 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 10 Sep 2020 11:19:30 +02:00

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: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200827114044.11173-9-a.darwish@linutronix.de
---
include/linux/seqlock.h | 36 +++++++++++++++---------------------
1 file changed, 15 insertions(+), 21 deletions(-)

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 88b917d..f2a7a46 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -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 */
}

/*