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sys_clock: Fix unsafe tick count usage

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The system tick count is a 64 bit quantity that gets updated from
interrupt context, meaning that it's dangerously non-atomic and has to
be locked.  The core kernel clock code did this right.

But the value was also exposed to the rest of the universe as a global
variable, and virtually nothing else was doing this correctly.  Even
in the timer ISRs themselves, the interrupts may be themselves
preempted (most of our architectures support nested interrupts) by
code that wants to set timeouts and inspect system uptime.

Define a z_tick_{get,set}() API, eliminate the old variable, and make
sure everyone uses the right mechanism.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2018-09-19 14:17:00 -07:00 • committed by Anas Nashif
commit 317178b88f
16 changed files with 105 additions and 100 deletions
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8
drivers/timer/arcv2_timer0.c
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@ -196,7 +196,7 @@ void _timer_int_handler(void *unused)
#ifdef CONFIG_TICKLESS_KERNEL
if (!programmed_ticks) {
if (_sys_clock_always_on) {
_sys_clock_tick_count = _get_elapsed_clock_time();
z_tick_set(_get_elapsed_clock_time());
program_max_cycles();
}
return;
@ -216,7 +216,7 @@ void _timer_int_handler(void *unused)
/* _sys_clock_tick_announce() could cause new programming */
if (!programmed_ticks && _sys_clock_always_on) {
_sys_clock_tick_count = _get_elapsed_clock_time();
z_tick_set(_get_elapsed_clock_time());
program_max_cycles();
}
#else
@ -280,7 +280,7 @@ void _set_time(u32_t time)
programmed_ticks = time > max_system_ticks ? max_system_ticks : time;
_sys_clock_tick_count = _get_elapsed_clock_time();
z_tick_set(_get_elapsed_clock_time());
timer0_limit_register_set(programmed_ticks * cycles_per_tick);
timer0_count_register_set(0);
@ -306,7 +306,7 @@ static inline u64_t get_elapsed_count(void)
elapsed = timer0_count_register_get();
}
elapsed += _sys_clock_tick_count * cycles_per_tick;
elapsed += z_tick_get() * cycles_per_tick;
return elapsed;
}