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bpf: Skip rcu_barrier() if rcu_trace_implies_rcu_gp() is true

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If there are pending rcu callback, free_mem_alloc() will use
rcu_barrier_tasks_trace() and rcu_barrier() to wait for the pending
__free_rcu_tasks_trace() and __free_rcu() callback.

If rcu_trace_implies_rcu_gp() is true, there will be no pending
__free_rcu(), so it will be OK to skip rcu_barrier() as well.

Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20221209010947.3130477-3-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Hou Tao 2022-12-09 09:09:47 +08:00 committed by Alexei Starovoitov
parent 0893d6007d
commit 822ed78fab
1 changed files with 9 additions and 1 deletions
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10
kernel/bpf/memalloc.c
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@ -464,9 +464,17 @@ static void free_mem_alloc(struct bpf_mem_alloc *ma)
{
/* waiting_for_gp lists was drained, but __free_rcu might
* still execute. Wait for it now before we freeing percpu caches.
*
* rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(),
* but rcu_barrier_tasks_trace() and rcu_barrier() below are only used
* to wait for the pending __free_rcu_tasks_trace() and __free_rcu(),
* so if call_rcu(head, __free_rcu) is skipped due to
* rcu_trace_implies_rcu_gp(), it will be OK to skip rcu_barrier() by
* using rcu_trace_implies_rcu_gp() as well.
*/
rcu_barrier_tasks_trace();
rcu_barrier();
if (!rcu_trace_implies_rcu_gp())
rcu_barrier();
free_mem_alloc_no_barrier(ma);
}