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sys/pm: Correctly access pm_blocker

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Replace `volatile` access to pm_blocker by guarding the accesses with
`irq_disable()` ... `irq_restore()`.

`volatile` does only guarantee that no compiler optimizations are performed on
a variable access, but does not provide atomic access. E.g. on systems with
a memory bus of less than 32 bit, the access to pm_blocker cannot be done
with a single CPU instruction. Thus, resorting to disabling IRQs is the easiest
and most portable way to actually achieve atomic access.
This commit is contained in:
Marian Buschsieweke 2020-04-29 11:14:00 +02:00
parent ba329daeee
commit 5ecafab83d
No known key found for this signature in database
GPG Key ID: 61F64C6599B1539F
1 changed files with 8 additions and 3 deletions
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11
sys/pm_layered/pm.c
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@ -36,11 +36,13 @@
/** /**
* @brief Global variable for keeping track of blocked modes * @brief Global variable for keeping track of blocked modes
*/ */
static volatile pm_blocker_t pm_blocker = { .val_u32 = PM_BLOCKER_INITIAL }; static pm_blocker_t pm_blocker = { .val_u32 = PM_BLOCKER_INITIAL };
void pm_set_lowest(void) void pm_set_lowest(void)
{ {
unsigned state = irq_disable();
pm_blocker_t blocker = pm_blocker; pm_blocker_t blocker = pm_blocker;
irq_restore(state);
unsigned mode = PM_NUM_MODES; unsigned mode = PM_NUM_MODES;
while (mode) { while (mode) {
if (blocker.val_u8[mode-1]) { if (blocker.val_u8[mode-1]) {
@ -50,7 +52,7 @@ void pm_set_lowest(void)
} }
/* set lowest mode if blocker is still the same */ /* set lowest mode if blocker is still the same */
unsigned state = irq_disable(); state = irq_disable();
if (blocker.val_u32 == pm_blocker.val_u32) { if (blocker.val_u32 == pm_blocker.val_u32) {
DEBUG("pm: setting mode %u\n", mode); DEBUG("pm: setting mode %u\n", mode);
pm_set(mode); pm_set(mode);
@ -81,7 +83,10 @@ void pm_unblock(unsigned mode)
pm_blocker_t pm_get_blocker(void) pm_blocker_t pm_get_blocker(void)
{ {
return pm_blocker; unsigned state = irq_disable();
pm_blocker_t result = pm_blocker;
irq_restore(state);
return result;
} }
#ifndef PROVIDES_PM_LAYERED_OFF #ifndef PROVIDES_PM_LAYERED_OFF