diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index 2891f94a11c6..87b261b87b0b 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -328,6 +328,7 @@ bool __percpu_counter_limited_add(struct percpu_counter *fbc, s64 limit, s64 amount, s32 batch) { s64 count; + s64 gcount; s64 unknown; unsigned long flags; bool good = false; @@ -338,11 +339,16 @@ bool __percpu_counter_limited_add(struct percpu_counter *fbc, local_irq_save(flags); unknown = batch * num_online_cpus(); count = __this_cpu_read(*fbc->counters); + /* + * Lockless on purpose: gcount may be stale, so this is only an + * approximation, bounded by the per-cpu slack ("unknown"). + */ + gcount = data_race(READ_ONCE(fbc->count)); /* Skip taking the lock when safe */ if (abs(count + amount) <= batch && - ((amount > 0 && fbc->count + unknown <= limit) || - (amount < 0 && fbc->count - unknown >= limit))) { + ((amount > 0 && gcount + unknown <= limit) || + (amount < 0 && gcount - unknown >= limit))) { this_cpu_add(*fbc->counters, amount); local_irq_restore(flags); return true;