diff options
-rw-r--r-- | include/linux/seqlock.h | 46 |
1 files changed, 29 insertions, 17 deletions
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 26e4925bc35b..632205ccc25d 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -85,23 +85,29 @@ static inline int write_tryseqlock(seqlock_t *sl) /* Start of read calculation -- fetch last complete writer token */ static __always_inline unsigned read_seqbegin(const seqlock_t *sl) { - unsigned ret = sl->sequence; + unsigned ret; + +repeat: + ret = sl->sequence; smp_rmb(); + if (unlikely(ret & 1)) { + cpu_relax(); + goto repeat; + } + return ret; } -/* Test if reader processed invalid data. - * If initial values is odd, - * then writer had already started when section was entered - * If sequence value changed - * then writer changed data while in section - * - * Using xor saves one conditional branch. +/* + * Test if reader processed invalid data. + * + * If sequence value changed then writer changed data while in section. */ -static __always_inline int read_seqretry(const seqlock_t *sl, unsigned iv) +static __always_inline int read_seqretry(const seqlock_t *sl, unsigned start) { smp_rmb(); - return (iv & 1) | (sl->sequence ^ iv); + + return (sl->sequence != start); } @@ -122,20 +128,26 @@ typedef struct seqcount { /* Start of read using pointer to a sequence counter only. */ static inline unsigned read_seqcount_begin(const seqcount_t *s) { - unsigned ret = s->sequence; + unsigned ret; + +repeat: + ret = s->sequence; smp_rmb(); + if (unlikely(ret & 1)) { + cpu_relax(); + goto repeat; + } return ret; } -/* Test if reader processed invalid data. - * Equivalent to: iv is odd or sequence number has changed. - * (iv & 1) || (*s != iv) - * Using xor saves one conditional branch. +/* + * Test if reader processed invalid data because sequence number has changed. */ -static inline int read_seqcount_retry(const seqcount_t *s, unsigned iv) +static inline int read_seqcount_retry(const seqcount_t *s, unsigned start) { smp_rmb(); - return (iv & 1) | (s->sequence ^ iv); + + return s->sequence != start; } |