commit 336ae1180df5f69b9e0fb6561bec01c5f64361cf
ARM: sched_clock: Load cycle count after epoch stabilizes
This looks applicable to stable-3.10, which load cycle count after epoch stabilizes,
The function was moved from arch/arm/kernel/sched_clock.c to kernel/time/sched_clock.c because of upgrading version.
The commit id is 336ae1180df5f69b9e0fb6561bec01c5f64361cf in 3.18.
I designed a test case for recurring this bug as follows:
CPU0 CPU1
---- ----
g_counter = 1;
.......
cyc = read_sched_clock()
cyc_to_sched_clock()
update_sched_clock()
...
cd.epoch_cyc = cyc;
g_counter = 2;
epoch_cyc = cd.epoch_cyc;
if(g_counter == 2)
printk("error!\n");
g_counter = 1;
...
epoch_ns + cyc_to_ns((cyc - epoch_cyc)
The bug will be proven to exist if the strings "error!" happen on screen.
I find that "error!" happen firstly on screen in thirty hours.
The patch for test is as follows:
--- a/sched_clock.c 2014-11-25 08:24:15.000000000 +0000
+++ b/sched_clock.c 2014-12-01 08:46:32.000000000 +0000
@@ -15,7 +15,7 @@
#include <linux/timer.h>
#include <asm/sched_clock.h>
-
+unsigned int g_counter = 0;
struct clock_data {
u64 epoch_ns;
u32 epoch_cyc;
@@ -68,11 +68,14 @@
*/
do {
epoch_cyc = cd.epoch_cyc;
+ if(g_counter == 2)
+ printk("error!\n");
+ g_counter = 1;
smp_rmb();
epoch_ns = cd.epoch_ns;
smp_rmb();
} while (epoch_cyc != cd.epoch_cyc_copy);
-
+
return epoch_ns + cyc_to_ns((cyc - epoch_cyc) & mask, cd.mult, cd.shift);
}
@@ -99,6 +102,7 @@
cd.epoch_ns = ns;
smp_wmb();
cd.epoch_cyc = cyc;
+ g_counter = 2;
raw_local_irq_restore(flags);
}
@@ -168,6 +172,7 @@
static unsigned long long notrace sched_clock_32(void)
{
u32 cyc = read_sched_clock();
+ g_counter = 1;
return cyc_to_sched_clock(cyc, sched_clock_mask);
}
Stephen Boyd (1):
ARM: sched_clock: Load cycle count after epoch stabilizes
arch/arm/kernel/sched_clock.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
--
1.7.9.5
--
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