From: Joel Fernandes (Google) Date: Mon, 25 May 2020 21:47:46 +0000 (+0200) Subject: rcu/tree: Skip entry into the page allocator for PREEMPT_RT X-Git-Tag: block-5.9-2020-08-14~74^2^2^3~14 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=4d2919411867848fab78c7cb13139e17ad8b85bc;p=linux-block.git rcu/tree: Skip entry into the page allocator for PREEMPT_RT 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 Reviewed-by: Uladzislau Rezki Co-developed-by: Uladzislau Rezki Signed-off-by: Uladzislau Rezki Signed-off-by: Joel Fernandes (Google) Signed-off-by: Uladzislau Rezki (Sony) Signed-off-by: Paul E. McKenney --- diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index c5de5adca0dd..e0425faf3b3b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -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); }