From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Date: Mon, 20 Jul 2020 17:55:10 +0200
Subject: seqlock: Reorder seqcount_t and seqlock_t API definitions
Patch-mainline: v5.9-rc1
Git-commit: f4a27cbcec90ac04ee60e04b222e1449dcdba0bd
References: bsc#1176564 bsc#1162702
The seqlock.h seqcount_t and seqlock_t API definitions are presented in
the chronological order of their development rather than the order that
makes most sense to readers. This makes it hard to follow and understand
the header file code.
Group and reorder all of the exported seqlock.h functions according to
their function.
First, group together the seqcount_t standard read path functions:
- __read_seqcount_begin()
- raw_read_seqcount_begin()
- read_seqcount_begin()
since each function is implemented exactly in terms of the one above
it. Then, group the special-case seqcount_t readers on their own as:
- raw_read_seqcount()
- raw_seqcount_begin()
since the only difference between the two functions is that the second
one masks the sequence counter LSB while the first one does not. Note
that raw_seqcount_begin() can actually be implemented in terms of
raw_read_seqcount(), which will be done in a follow-up commit.
Then, group the seqcount_t write path functions, instead of injecting
unrelated seqcount_t latch functions between them, and order them as:
- raw_write_seqcount_begin()
- raw_write_seqcount_end()
- write_seqcount_begin_nested()
- write_seqcount_begin()
- write_seqcount_end()
- raw_write_seqcount_barrier()
- write_seqcount_invalidate()
which is the expected natural order. This also isolates the seqcount_t
latch functions into their own area, at the end of the sequence counters
section, and before jumping to the next one: sequential locks
(seqlock_t).
Do a similar grouping and reordering for seqlock_t "locking" readers vs.
the "conditionally locking or lockless" ones.
No implementation code was changed in any of the reordering above.
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/20200720155530.1173732-5-a.darwish@linutronix.de
[dwagner: updated context due to missing kcsan bits]
Acked-by: Daniel Wagner <dwagner@suse.de>
---
include/linux/seqlock.h | 118 +++++++++++++++++++++++-------------------------
1 file changed, 58 insertions(+), 60 deletions(-)
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -112,22 +112,6 @@ static inline unsigned __read_seqcount_b
}
/**
- * raw_read_seqcount - Read the raw seqcount
- * @s: pointer to seqcount_t
- * Returns: count to be passed to read_seqcount_retry
- *
- * raw_read_seqcount opens a read critical section of the given
- * seqcount without any lockdep checking and without checking or
- * masking the LSB. Calling code is responsible for handling that.
- */
-static inline unsigned raw_read_seqcount(const seqcount_t *s)
-{
- unsigned ret = READ_ONCE(s->sequence);
- smp_rmb();
- return ret;
-}
-
-/**
* raw_read_seqcount_begin - start seq-read critical section w/o lockdep
* @s: pointer to seqcount_t
* Returns: count to be passed to read_seqcount_retry
@@ -159,6 +143,22 @@ static inline unsigned read_seqcount_beg
}
/**
+ * raw_read_seqcount - Read the raw seqcount
+ * @s: pointer to seqcount_t
+ * Returns: count to be passed to read_seqcount_retry
+ *
+ * raw_read_seqcount opens a read critical section of the given
+ * seqcount without any lockdep checking and without checking or
+ * masking the LSB. Calling code is responsible for handling that.
+ */
+static inline unsigned raw_read_seqcount(const seqcount_t *s)
+{
+ unsigned ret = READ_ONCE(s->sequence);
+ smp_rmb();
+ return ret;
+}
+
+/**
* raw_seqcount_begin - begin a seq-read critical section
* @s: pointer to seqcount_t
* Returns: count to be passed to read_seqcount_retry
@@ -214,8 +214,6 @@ static inline int read_seqcount_retry(co
return __read_seqcount_retry(s, start);
}
-
-
static inline void raw_write_seqcount_begin(seqcount_t *s)
{
s->sequence++;
@@ -276,6 +274,19 @@ static inline void raw_write_seqcount_ba
s->sequence++;
}
+/**
+ * write_seqcount_invalidate - invalidate in-progress read-side seq operations
+ * @s: pointer to seqcount_t
+ *
+ * After write_seqcount_invalidate, no read-side seq operations will complete
+ * successfully and see data older than this.
+ */
+static inline void write_seqcount_invalidate(seqcount_t *s)
+{
+ smp_wmb();
+ s->sequence+=2;
+}
+
static inline int raw_read_seqcount_latch(seqcount_t *s)
{
/* Pairs with the first smp_wmb() in raw_write_seqcount_latch() */
@@ -388,19 +399,6 @@ static inline void write_seqcount_end(se
raw_write_seqcount_end(s);
}
-/**
- * write_seqcount_invalidate - invalidate in-progress read-side seq operations
- * @s: pointer to seqcount_t
- *
- * After write_seqcount_invalidate, no read-side seq operations will complete
- * successfully and see data older than this.
- */
-static inline void write_seqcount_invalidate(seqcount_t *s)
-{
- smp_wmb();
- s->sequence+=2;
-}
-
/*
* Sequential locks (seqlock_t)
*
@@ -519,35 +517,6 @@ static inline void read_sequnlock_excl(s
spin_unlock(&sl->lock);
}
-/**
- * read_seqbegin_or_lock - begin a sequence number check or locking block
- * @lock: sequence lock
- * @seq : sequence number to be checked
- *
- * First try it once optimistically without taking the lock. If that fails,
- * take the lock. The sequence number is also used as a marker for deciding
- * whether to be a reader (even) or writer (odd).
- * N.B. seq must be initialized to an even number to begin with.
- */
-static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
-{
- if (!(*seq & 1)) /* Even */
- *seq = read_seqbegin(lock);
- else /* Odd */
- read_seqlock_excl(lock);
-}
-
-static inline int need_seqretry(seqlock_t *lock, int seq)
-{
- return !(seq & 1) && read_seqretry(lock, seq);
-}
-
-static inline void done_seqretry(seqlock_t *lock, int seq)
-{
- if (seq & 1)
- read_sequnlock_excl(lock);
-}
-
static inline void read_seqlock_excl_bh(seqlock_t *sl)
{
spin_lock_bh(&sl->lock);
@@ -585,6 +554,35 @@ read_sequnlock_excl_irqrestore(seqlock_t
spin_unlock_irqrestore(&sl->lock, flags);
}
+/**
+ * read_seqbegin_or_lock - begin a sequence number check or locking block
+ * @lock: sequence lock
+ * @seq : sequence number to be checked
+ *
+ * First try it once optimistically without taking the lock. If that fails,
+ * take the lock. The sequence number is also used as a marker for deciding
+ * whether to be a reader (even) or writer (odd).
+ * N.B. seq must be initialized to an even number to begin with.
+ */
+static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
+{
+ if (!(*seq & 1)) /* Even */
+ *seq = read_seqbegin(lock);
+ else /* Odd */
+ read_seqlock_excl(lock);
+}
+
+static inline int need_seqretry(seqlock_t *lock, int seq)
+{
+ return !(seq & 1) && read_seqretry(lock, seq);
+}
+
+static inline void done_seqretry(seqlock_t *lock, int seq)
+{
+ if (seq & 1)
+ read_sequnlock_excl(lock);
+}
+
static inline unsigned long
read_seqbegin_or_lock_irqsave(seqlock_t *lock, int *seq)
{