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module-rt: Handle realtime sched check edge cases

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The policy can of course be higher than zero if the current thread uses
anything other than `SCHED_OTHER`, and `SCHED_RESET_ON_FORK` needs to be
set according to the old policy or we'll either run into errors or cause
unwanted side effects.
This commit is contained in:
Robbert van der Helm 2022-01-19 16:10:02 +01:00
parent e60f62e69b
commit 5d890435b4
1 changed files with 17 additions and 6 deletions
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23
src/modules/module-rt.c
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@ -482,23 +482,34 @@ static const struct pw_impl_module_events module_events = {
*/ */
static bool check_realtime_priviliges(rlim_t priority) static bool check_realtime_priviliges(rlim_t priority)
{ {
int old_policy;
struct sched_param old_sched_params;
int new_policy = REALTIME_POLICY;
struct sched_param new_sched_params;
/* We could check `RLIMIT_RTPRIO`, but the BSDs generally don't have /* We could check `RLIMIT_RTPRIO`, but the BSDs generally don't have
* that available, and there are also other ways to use realtime * that available, and there are also other ways to use realtime
* scheduling without that rlimit being set such as `CAP_SYS_NICE` or * scheduling without that rlimit being set such as `CAP_SYS_NICE` or
* running as root. Instead of checking a bunch of preconditions, we * running as root. Instead of checking a bunch of preconditions, we
* just try if setting realtime scheduling works or not. */ * just try if setting realtime scheduling works or not. */
int old_scheduler; if ((old_policy = sched_getscheduler(0)) < 0 ||
struct sched_param old_sched_params;
if ((old_scheduler = sched_getscheduler(0)) != 0 ||
sched_getparam(0, &old_sched_params) != 0) { sched_getparam(0, &old_sched_params) != 0) {
return false; return false;
} }
struct sched_param new_sched_params; /* If the current scheduling policy has `SCHED_RESET_ON_FORK` set, then
* this also needs to be set here or `sched_setscheduler()` will return
* an error code. Similarly, if it is not set, then we don't want to set
* it here as it would irreversible change the current thread's
* scheduling policy. */
spa_zero(new_sched_params); spa_zero(new_sched_params);
new_sched_params.sched_priority = priority; new_sched_params.sched_priority = priority;
if (sched_setscheduler(0, REALTIME_POLICY, &new_sched_params) == 0) { if ((old_policy & PW_SCHED_RESET_ON_FORK) != 0) {
sched_setscheduler(0, old_scheduler, &old_sched_params); new_policy |= PW_SCHED_RESET_ON_FORK;
}
if (sched_setscheduler(0, new_policy, &new_sched_params) == 0) {
sched_setscheduler(0, old_policy, &old_sched_params);
return true; return true;
} else { } else {
return false; return false;