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Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull timer fix from Thomas Gleixner:
 "Serialize the registration of a new sched_clock in the currently ARM
  only generic sched_clock facilty to avoid sched_clock havoc"

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched_clock: Prevent callers from seeing half-updated data
This commit is contained in:
Linus Torvalds 2014-02-23 14:17:08 -08:00
parent 208937fdcf 5ae8aabeae
commit b2880eb83d
1 changed files with 29 additions and 17 deletions
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46
kernel/time/sched_clock.c
View File

@ -116,20 +116,42 @@ static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
void __init sched_clock_register(u64 (*read)(void), int bits,
unsigned long rate)
{
u64 res, wrap, new_mask, new_epoch, cyc, ns;
u32 new_mult, new_shift;
ktime_t new_wrap_kt;
unsigned long r;
u64 res, wrap;
char r_unit;
if (cd.rate > rate)
return;
WARN_ON(!irqs_disabled());
read_sched_clock = read;
sched_clock_mask = CLOCKSOURCE_MASK(bits);
cd.rate = rate;
/* calculate the mult/shift to convert counter ticks to ns. */
clocks_calc_mult_shift(&cd.mult, &cd.shift, rate, NSEC_PER_SEC, 3600);
clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
new_mask = CLOCKSOURCE_MASK(bits);
/* calculate how many ns until we wrap */
wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask);
new_wrap_kt = ns_to_ktime(wrap - (wrap >> 3));
/* update epoch for new counter and update epoch_ns from old counter*/
new_epoch = read();
cyc = read_sched_clock();
ns = cd.epoch_ns + cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
cd.mult, cd.shift);
raw_write_seqcount_begin(&cd.seq);
read_sched_clock = read;
sched_clock_mask = new_mask;
cd.rate = rate;
cd.wrap_kt = new_wrap_kt;
cd.mult = new_mult;
cd.shift = new_shift;
cd.epoch_cyc = new_epoch;
cd.epoch_ns = ns;
raw_write_seqcount_end(&cd.seq);
r = rate;
if (r >= 4000000) {
@ -141,22 +163,12 @@ void __init sched_clock_register(u64 (*read)(void), int bits,
} else
r_unit = ' ';
/* calculate how many ns until we wrap */
wrap = clocks_calc_max_nsecs(cd.mult, cd.shift, 0, sched_clock_mask);
cd.wrap_kt = ns_to_ktime(wrap - (wrap >> 3));
/* calculate the ns resolution of this counter */
res = cyc_to_ns(1ULL, cd.mult, cd.shift);
res = cyc_to_ns(1ULL, new_mult, new_shift);
pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
bits, r, r_unit, res, wrap);
update_sched_clock();
/*
* Ensure that sched_clock() starts off at 0ns
*/
cd.epoch_ns = 0;
/* Enable IRQ time accounting if we have a fast enough sched_clock */
if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
enable_sched_clock_irqtime();