On Fri, Sep 04, 2020 at 05:32:30PM +0200, Ahmed S. Darwish wrote:
> @@ -406,13 +443,20 @@ static inline int read_seqcount_t_retry(const
> seqcount_t *s, unsigned start)
> return __read_seqcount_t_retry(s, start);
> }
>
> +/*
> + * Enforce non-preemptibility for all seqcount_LOCKNAME_t writers. Don't
> + * do it for PREEMPT_RT, for the reasons outlined at __SEQ_LOCK().
> + */
> +#define __seq_enforce_writer_non_preemptibility(s) \
> + (!IS_ENABLED(CONFIG_PREEMPT_RT) && __seqcount_lock_preemptible(s))
> +
> /**
> * raw_write_seqcount_begin() - start a seqcount_t write section w/o lockdep
> * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
> */
> #define raw_write_seqcount_begin(s) \
> do { \
> - if (__seqcount_lock_preemptible(s)) \
> + if (__seq_enforce_writer_non_preemptibility(s)) \
> preempt_disable(); \
> \
> raw_write_seqcount_t_begin(__seqcount_ptr(s)); \
> @@ -433,7 +477,7 @@ static inline void raw_write_seqcount_t_begin(seqcount_t
> *s)
> do { \
> raw_write_seqcount_t_end(__seqcount_ptr(s)); \
> \
> - if (__seqcount_lock_preemptible(s)) \
> + if (__seq_enforce_writer_non_preemptibility(s)) \
> preempt_enable(); \
> } while (0)
>
> @@ -456,7 +500,7 @@ static inline void raw_write_seqcount_t_end(seqcount_t *s)
> do { \
> __seqcount_assert_lock_held(s); \
> \
> - if (__seqcount_lock_preemptible(s)) \
> + if (__seq_enforce_writer_non_preemptibility(s)) \
> preempt_disable(); \
> \
> write_seqcount_t_begin_nested(__seqcount_ptr(s), subclass); \
> @@ -483,7 +527,7 @@ static inline void
> write_seqcount_t_begin_nested(seqcount_t *s, int subclass)
> do { \
> __seqcount_assert_lock_held(s); \
> \
> - if (__seqcount_lock_preemptible(s)) \
> + if (__seq_enforce_writer_non_preemptibility(s)) \
> preempt_disable(); \
> \
> write_seqcount_t_begin(__seqcount_ptr(s)); \
> @@ -504,7 +548,7 @@ static inline void write_seqcount_t_begin(seqcount_t *s)
> do { \
> write_seqcount_t_end(__seqcount_ptr(s)); \
> \
> - if (__seqcount_lock_preemptible(s)) \
> + if (__seq_enforce_writer_non_preemptibility(s)) \
> preempt_enable(); \
> } while (0)
I've replaced the above with the below, afaict there were no users of
__seqcount_lock_preemptible() left.
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -228,7 +228,11 @@ __seqprop_##lockname##_sequence(const se
static __always_inline bool \
__seqprop_##lockname##_preemptible(const seqcount_##lockname##_t *s) \
{ \
- return preemptible; \
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
+ return preemptible; \
+ \
+ /* PREEMPT_RT relies on the above LOCK+UNLOCK */ \
+ return false; \
} \
\
static __always_inline void \
