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rcu/tree: Skip entry into the page allocator for PREEMPT_RT

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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>
This commit is contained in:
Joel Fernandes (Google) 2020-05-25 23:47:46 +02:00 committed by Paul E. McKenney
parent 8ac88f7177
commit 4d29194118
1 changed files with 12 additions and 0 deletions
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12
kernel/rcu/tree.c
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@ -3202,6 +3202,18 @@ 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);
}