From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
To: LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Paul E . McKenney" <paulmck@kernel.org>,
"Theodore Y . Ts'o" <tytso@mit.edu>,
Matthew Wilcox <willy@infradead.org>,
Joel Fernandes <joel@joelfernandes.org>,
RCU <rcu@vger.kernel.org>, Uladzislau Rezki <urezki@gmail.com>,
Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH v2 02/16] rcu/tree: Skip entry into the page allocator for PREEMPT_RT
Date: Mon, 25 May 2020 23:47:46 +0200 [thread overview]
Message-ID: <20200525214800.93072-3-urezki@gmail.com> (raw)
In-Reply-To: <20200525214800.93072-1-urezki@gmail.com>
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>
---
kernel/rcu/tree.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6e967a9d6704..d28010cf158b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3068,6 +3068,18 @@ 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
next prev parent reply other threads:[~2020-05-25 21:48 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-25 21:47 [PATCH v2 00/16] Introduce kvfree_rcu(1 or 2 arguments) Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 01/16] rcu/tree: Keep kfree_rcu() awake during lock contention Uladzislau Rezki (Sony)
2020-05-25 21:47 ` Uladzislau Rezki (Sony) [this message]
2020-05-25 21:47 ` [PATCH v2 03/16] rcu/tree: Repeat the monitor if any free channel is busy Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 04/16] rcu/tree: Make debug_objects logic independent of rcu_head Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 05/16] rcu/tree: Simplify KFREE_BULK_MAX_ENTR macro Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 06/16] rcu/tree: Move kfree_rcu_cpu locking/unlocking to separate functions Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 07/16] rcu/tree: Use static initializer for krc.lock Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 08/16] rcu/tree: cache specified number of objects Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs Uladzislau Rezki (Sony)
2020-06-17 23:46 ` Paul E. McKenney
2020-06-18 0:52 ` Matthew Wilcox
2020-06-18 3:18 ` Paul E. McKenney
2020-06-18 17:35 ` Uladzislau Rezki
2020-06-18 17:57 ` Paul E. McKenney
2020-06-18 18:34 ` Uladzislau Rezki
2020-06-18 19:03 ` Paul E. McKenney
2020-06-18 20:35 ` Uladzislau Rezki
2020-06-18 20:38 ` Matthew Wilcox
2020-06-18 21:17 ` Uladzislau Rezki
2020-06-18 21:34 ` Paul E. McKenney
2020-06-19 15:46 ` Uladzislau Rezki
2020-06-19 16:25 ` Paul E. McKenney
2020-06-22 19:04 ` Uladzislau Rezki
2020-06-22 19:53 ` Paul E. McKenney
2020-06-30 17:46 ` Uladzislau Rezki
2020-06-18 17:30 ` Uladzislau Rezki
2020-06-18 17:35 ` Matthew Wilcox
2020-06-18 20:03 ` Uladzislau Rezki
2020-06-18 17:25 ` Uladzislau Rezki
2020-06-18 17:32 ` Paul E. McKenney
2020-06-18 17:56 ` Uladzislau Rezki
2020-06-18 18:15 ` Matthew Wilcox
2020-06-18 18:23 ` Uladzislau Rezki
2020-06-18 18:37 ` Matthew Wilcox
2020-06-18 18:48 ` Uladzislau Rezki
2020-05-25 21:47 ` [PATCH v2 10/16] rcu/tiny: support vmalloc in tiny-RCU Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 11/16] rcu: Rename *_kfree_callback/*_kfree_rcu_offset/kfree_call_* Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 12/16] mm/list_lru.c: Rename kvfree_rcu() to local variant Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 13/16] rcu: Introduce 2 arg kvfree_rcu() interface Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 14/16] rcu: Support reclaim for head-less object Uladzislau Rezki (Sony)
2020-05-25 21:47 ` [PATCH v2 15/16] rcu: Introduce single argument kvfree_rcu() interface Uladzislau Rezki (Sony)
2020-05-25 21:48 ` [PATCH v2 16/16] lib/test_vmalloc.c: Add test cases for kvfree_rcu() Uladzislau Rezki (Sony)
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