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McKenney" , rcu@vger.kernel.org, Steven Rostedt Subject: [PATCH rcu/dev -fixes 2/4] rcu/tree: Skip entry into the page allocator for PREEMPT_RT Date: Mon, 20 Apr 2020 11:38:35 -0400 Message-Id: <20200420153837.194532-3-joel@joelfernandes.org> X-Mailer: git-send-email 2.26.1.301.g55bc3eb7cb9-goog In-Reply-To: <20200420153837.194532-1-joel@joelfernandes.org> References: <20200420153837.194532-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org 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 Co-developed-by: Uladzislau Rezki Signed-off-by: Uladzislau Rezki Signed-off-by: Joel Fernandes (Google) --- kernel/rcu/tree.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cf68d3d9f5b81..cd61649e1b001 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); } -- 2.26.1.301.g55bc3eb7cb9-goog