We're going to increase the cyc value to 64 bits in the near
future. Doing that is going to break the custom seqcount
implementation in the sched_clock code because 64 bit numbers
aren't guaranteed to be atomic. Replace the cyc_copy with a
seqcount to avoid this problem.
Cc: Russell King <li...@arm.linux.org.uk>
Signed-off-by: Stephen Boyd <sb...@codeaurora.org>
---
kernel/time/sched_clock.c | 27 ++++++++-------------------
1 file changed, 8 insertions(+), 19 deletions(-)
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index a326f27..396f7b9 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -14,11 +14,12 @@
#include <linux/syscore_ops.h>
#include <linux/timer.h>
#include <linux/sched_clock.h>
+#include <linux/seqlock.h>
struct clock_data {
u64 epoch_ns;
u32 epoch_cyc;
- u32 epoch_cyc_copy;
+ seqcount_t seq;
unsigned long rate;
u32 mult;
u32 shift;
@@ -54,23 +55,16 @@ static unsigned long long notrace sched_clock_32(void)
u64 epoch_ns;
u32 epoch_cyc;
u32 cyc;
+ unsigned long seq;
if (cd.suspended)
return cd.epoch_ns;
- /*
- * Load the epoch_cyc and epoch_ns atomically. We do this by
- * ensuring that we always write epoch_cyc, epoch_ns and
- * epoch_cyc_copy in strict order, and read them in strict order.
- * If epoch_cyc and epoch_cyc_copy are not equal, then we're in
- * the middle of an update, and we should repeat the load.
- */
do {
+ seq = read_seqcount_begin(&cd.seq);
epoch_cyc = cd.epoch_cyc;
- smp_rmb();
epoch_ns = cd.epoch_ns;
- smp_rmb();
- } while (epoch_cyc != cd.epoch_cyc_copy);
+ } while (read_seqcount_retry(&cd.seq, seq));
cyc = read_sched_clock();
cyc = (cyc - epoch_cyc) & sched_clock_mask;
@@ -90,16 +84,12 @@ static void notrace update_sched_clock(void)
ns = cd.epoch_ns +
cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
cd.mult, cd.shift);
- /*
- * Write epoch_cyc and epoch_ns in a way that the update is
- * detectable in cyc_to_fixed_sched_clock().
- */
+
raw_local_irq_save(flags);
- cd.epoch_cyc_copy = cyc;
- smp_wmb();
+ write_seqcount_begin(&cd.seq);
cd.epoch_ns = ns;
- smp_wmb();
cd.epoch_cyc = cyc;
+ write_seqcount_end(&cd.seq);
raw_local_irq_restore(flags);
}
@@ -195,7 +185,6 @@ static int sched_clock_suspend(void)
static void sched_clock_resume(void)
{
cd.epoch_cyc = read_sched_clock();
- cd.epoch_cyc_copy = cd.epoch_cyc;
cd.suspended = false;
}
--
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