Messages in this thread Patch in this message | | | From | paulmck@kernel ... | Subject | [PATCH tip/core/rcu 03/17] rcu/tree: Skip entry into the page allocator for PREEMPT_RT | Date | Wed, 24 Jun 2020 13:12:12 -0700 |
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From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To keep the kfree_rcu() code working in purely atomic sections on RT, such as non-threaded IRQ handlers and raw spinlock sections, avoid calling into the page allocator which uses sleeping locks on RT.
In fact, even if the caller is preemptible, the kfree_rcu() code is not, as the krcp->lock is a raw spinlock.
Calling into the page allocator is optional and avoiding it should be Ok, especially with the page pre-allocation support in future patches. Such pre-allocation would further avoid the a need for a dynamically allocated page in the first place.
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Reviewed-by: Uladzislau Rezki <urezki@gmail.com> Co-developed-by: Uladzislau Rezki <urezki@gmail.com> Signed-off-by: Uladzislau Rezki <urezki@gmail.com> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> --- kernel/rcu/tree.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 64592b4..dbdd509 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3184,6 +3184,18 @@ 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); } -- 2.9.5
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