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Prevent one CPU from getting chosen by concurrent forks

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One CPU could be chosen by concurrent forks because CPU selection and
runq addition are not done atomicly. So this fix makes the two steps
atomic.

Change-Id: Ib6b75ad655789385d13207e0a47fa4717dec854a
This commit is contained in:
Masamichi Takagi
2018-09-04 09:33:10 +09:00
parent 82914c6a2e
commit 0b0b7b03d7
4 changed files with 26 additions and 10 deletions
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14
arch/x86_64/kernel/syscall.c
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@ -93,21 +93,23 @@ extern int num_processors;
int obtain_clone_cpuid(cpu_set_t *cpu_set) {
int min_queue_len = -1;
int cpu, min_cpu = -1;
unsigned long irqstate;
irqstate = ihk_mc_spinlock_lock(&runq_reservation_lock);
/* Find the first allowed core with the shortest run queue */
for (cpu = 0; cpu < num_processors; ++cpu) {
struct cpu_local_var *v;
unsigned long irqstate;
if (!CPU_ISSET(cpu, cpu_set)) continue;
v = get_cpu_local_var(cpu);
irqstate = ihk_mc_spinlock_lock(&v->runq_lock);
if (min_queue_len == -1 || v->runq_len < min_queue_len) {
min_queue_len = v->runq_len;
ihk_mc_spinlock_lock_noirq(&v->runq_lock);
dkprintf("%s: cpu=%d,runq_len=%d,runq_reserved=%d\n", __FUNCTION__, cpu, v->runq_len, v->runq_reserved);
if (min_queue_len == -1 || v->runq_len + v->runq_reserved < min_queue_len) {
min_queue_len = v->runq_len + v->runq_reserved;
min_cpu = cpu;
}
ihk_mc_spinlock_unlock(&v->runq_lock, irqstate);
ihk_mc_spinlock_unlock_noirq(&v->runq_lock);
if (min_queue_len == 0)
break;
@ -116,7 +118,9 @@ int obtain_clone_cpuid(cpu_set_t *cpu_set) {
if (min_cpu != -1) {
if (get_cpu_local_var(min_cpu)->status != CPU_STATUS_RESERVED)
get_cpu_local_var(min_cpu)->status = CPU_STATUS_RESERVED;
__sync_fetch_and_add(&get_cpu_local_var(min_cpu)->runq_reserved, 1);
}
ihk_mc_spinlock_unlock(&runq_reservation_lock, irqstate);
return min_cpu;
}