[PATCH v1 6/8] x86/tsc: Use seqcount_latch_t

[Ahmed S. Darwish]

Latch sequence counters have unique read and write APIs, and thus
seqcount_latch_t was recently introduced at seqlock.h.

Use that new data type instead of plain seqcount_t. This adds the
necessary type-safety and ensures that only latching-safe seqcount APIs
are to be used.

Signed-off-by: Ahmed S. Darwish <a.darw...@linutronix.de>
---
 arch/x86/kernel/tsc.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 49d925043171..cbf17e9f1d03 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -54,7 +54,7 @@ struct clocksource *art_related_clocksource;
 
 struct cyc2ns {
        struct cyc2ns_data data[2];     /*  0 + 2*16 = 32 */
-       seqcount_t         seq;         /* 32 + 4    = 36 */
+       seqcount_latch_t   seq;         /* 32 + 4    = 36 */
 
 }; /* fits one cacheline */
 
@@ -68,19 +68,21 @@ early_param("tsc_early_khz", tsc_early_khz_setup);
 
 __always_inline void cyc2ns_read_begin(struct cyc2ns_data *data)
 {
+       seqcount_latch_t *seqcount;
        int seq, idx;
 
        preempt_disable_notrace();
 
+       seqcount = &this_cpu_ptr(&cyc2ns)->seq;
        do {
-               seq = this_cpu_read(cyc2ns.seq.sequence);
+               seq = raw_read_seqcount_latch(seqcount);
                idx = seq & 1;
 
                data->cyc2ns_offset = 
this_cpu_read(cyc2ns.data[idx].cyc2ns_offset);
                data->cyc2ns_mul    = 
this_cpu_read(cyc2ns.data[idx].cyc2ns_mul);
                data->cyc2ns_shift  = 
this_cpu_read(cyc2ns.data[idx].cyc2ns_shift);
 
-       } while (unlikely(seq != this_cpu_read(cyc2ns.seq.sequence)));
+       } while (read_seqcount_latch_retry(seqcount, seq));
 }
 
 __always_inline void cyc2ns_read_end(void)
@@ -186,7 +188,7 @@ static void __init cyc2ns_init_boot_cpu(void)
 {
        struct cyc2ns *c2n = this_cpu_ptr(&cyc2ns);
 
-       seqcount_init(&c2n->seq);
+       seqcount_latch_init(&c2n->seq);
        __set_cyc2ns_scale(tsc_khz, smp_processor_id(), rdtsc());
 }
 
@@ -203,7 +205,7 @@ static void __init cyc2ns_init_secondary_cpus(void)
 
        for_each_possible_cpu(cpu) {
                if (cpu != this_cpu) {
-                       seqcount_init(&c2n->seq);
+                       seqcount_latch_init(&c2n->seq);
                        c2n = per_cpu_ptr(&cyc2ns, cpu);
                        c2n->data[0] = data[0];
                        c2n->data[1] = data[1];
-- 
2.28.0