From: "Joel Fernandes (Google)" <[email protected]> To keep kfree_rcu() path working on raw non-preemptible sections, prevent the optional entry into the allocator as it uses sleeping locks. In fact, even if the caller of kfree_rcu() is preemptible, this path still is not, as krcp->lock is a raw spinlock as done in previous patches. With additional page pre-allocation in the works, hitting this return is going to be much less likely soon so just prevent it for now so that PREEMPT_RT does not break. Note that page allocation here is an optimization and skipping it still makes kfree_rcu() work.
Cc: Sebastian Andrzej Siewior <[email protected]> Reviewed-by: Uladzislau Rezki <[email protected]> Co-developed-by: Uladzislau Rezki <[email protected]> Signed-off-by: Uladzislau Rezki <[email protected]> Signed-off-by: Joel Fernandes (Google) <[email protected]> Signed-off-by: Uladzislau Rezki (Sony) <[email protected]> --- kernel/rcu/tree.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cf68d3d9f5b8..cd61649e1b00 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3092,6 +3092,18 @@ kfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, if (!bnode) { WARN_ON_ONCE(sizeof(struct kfree_rcu_bulk_data) > PAGE_SIZE); + /* + * To keep this path working on raw non-preemptible + * sections, prevent the optional entry into the + * allocator as it uses sleeping locks. In fact, even + * if the caller of kfree_rcu() is preemptible, this + * path still is not, as krcp->lock is a raw spinlock. + * With additional page pre-allocation in the works, + * hitting this return is going to be much less likely. + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + return false; + bnode = (struct kfree_rcu_bulk_data *) __get_free_page(GFP_NOWAIT | __GFP_NOWARN); } -- 2.20.1
