Function steal_tags() might miss a bit in cpus_have_tags due to unsynchronized access from percpu_ida_free(). As result, function percpu_ida_alloc() might enter unwakable sleep. This update adds memory barriers to prevent the described scenario.
In fact, accesses to cpus_have_tags are fenced by prepare_to_wait() and wake_up() calls at the moment and the aforementioned sequence does not appear could hit. Nevertheless, explicit memory barriers still seem justifiable. Signed-off-by: Alexander Gordeev <[email protected]> --- lib/percpu_ida.c | 12 ++++++++++-- 1 files changed, 10 insertions(+), 2 deletions(-) diff --git a/lib/percpu_ida.c b/lib/percpu_ida.c index b0698ea..96cfacf 100644 --- a/lib/percpu_ida.c +++ b/lib/percpu_ida.c @@ -68,6 +68,11 @@ static inline void steal_tags(struct percpu_ida *pool, unsigned cpus_have_tags, cpu = pool->cpu_last_stolen; struct percpu_ida_cpu *remote; + /* + * Pairs with smp_wmb() in percpu_ida_free() + */ + smp_rmb(); + for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags); cpus_have_tags * pool->percpu_max_size > pool->nr_tags / 2; cpus_have_tags--) { @@ -231,8 +236,11 @@ void percpu_ida_free(struct percpu_ida *pool, unsigned tag) spin_unlock(&tags->lock); if (nr_free == 1) { - cpumask_set_cpu(smp_processor_id(), - &pool->cpus_have_tags); + cpumask_set_cpu(smp_processor_id(), &pool->cpus_have_tags); + /* + * Pairs with smp_rmb() in steal_tags() + */ + smp_wmb(); wake_up(&pool->wait); } -- 1.7.7.6 -- Regards, Alexander Gordeev [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
