linux-kernel - [PATCH v1 2/6] rcu: introduce kvfree

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Date:   Sun, 15 Mar 2020 19:18:36 +0100
From:   "Uladzislau Rezki (Sony)" <urezki@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Cc:     RCU <rcu@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: [PATCH v1 2/6] rcu: introduce kvfree_rcu() interface

kvfree_rcu() can deal with an allocated memory that is obtained
via kvmalloc(). It can return two types of allocated memory or
"pointers", one can belong to regular SLAB allocator and another
one can be vmalloc one. It depends on requested size and memory
pressure.

Based on that, two streams are split, thus if a pointer belongs
to vmalloc allocator it is queued to the list, otherwise SLAB
one is queued into "bulk array" for further processing.

The main reason of such splitting is:
    a) to distinguish kmalloc()/vmalloc() ptrs;
    b) there is no vmalloc_bulk() interface.

As of now we have list_lru.c user that needs such interface,
also there will be new comers. Apart of that it is preparation
to have a head-less variant later.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 include/linux/rcupdate.h |  9 +++++++++
 kernel/rcu/tiny.c        |  3 ++-
 kernel/rcu/tree.c        | 17 ++++++++++++-----
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 2be97a83f266..bb270221dbdc 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -845,6 +845,15 @@ do {									\
 		__kfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
 } while (0)
 
+/**
+ * kvfree_rcu() - kvfree an object after a grace period.
+ * @ptr:	pointer to kvfree
+ * @rhf:	the name of the struct rcu_head within the type of @ptr.
+ *
+ * Same as kfree_rcu(), just simple alias.
+ */
+#define kvfree_rcu(ptr, rhf) kfree_rcu(ptr, rhf)
+
 /*
  * Place this after a lock-acquisition primitive to guarantee that
  * an UNLOCK+LOCK pair acts as a full barrier.  This guarantee applies
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index dd572ce7c747..4b99f7b88bee 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -23,6 +23,7 @@
 #include <linux/cpu.h>
 #include <linux/prefetch.h>
 #include <linux/slab.h>
+#include <linux/mm.h>
 
 #include "rcu.h"
 
@@ -86,7 +87,7 @@ static inline bool rcu_reclaim_tiny(struct rcu_head *head)
 	rcu_lock_acquire(&rcu_callback_map);
 	if (__is_kfree_rcu_offset(offset)) {
 		trace_rcu_invoke_kfree_callback("", head, offset);
-		kfree((void *)head - offset);
+		kvfree((void *)head - offset);
 		rcu_lock_release(&rcu_callback_map);
 		return true;
 	}
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2f4c91a3713a..1c0a73616872 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2899,9 +2899,9 @@ static void kfree_rcu_work(struct work_struct *work)
 	}
 
 	/*
-	 * Emergency case only. It can happen under low memory
-	 * condition when an allocation gets failed, so the "bulk"
-	 * path can not be temporary maintained.
+	 * vmalloc() pointers end up here also emergency case. It can
+	 * happen under low memory condition when an allocation gets
+	 * failed, so the "bulk" path can not be temporary maintained.
 	 */
 	for (; head; head = next) {
 		unsigned long offset = (unsigned long)head->func;
@@ -2912,7 +2912,7 @@ static void kfree_rcu_work(struct work_struct *work)
 		trace_rcu_invoke_kfree_callback(rcu_state.name, head, offset);
 
 		if (!WARN_ON_ONCE(!__is_kfree_rcu_offset(offset)))
-			kfree((void *)head - offset);
+			kvfree((void *)head - offset);
 
 		rcu_lock_release(&rcu_callback_map);
 		cond_resched_tasks_rcu_qs();
@@ -3084,10 +3084,17 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 	}
 
 	/*
+	 * We do not queue vmalloc pointers into array,
+	 * instead they are just queued to the list. We
+	 * do it because of:
+	 *    a) to distinguish kmalloc()/vmalloc() ptrs;
+	 *    b) there is no vmalloc_bulk() interface.
+	 *
 	 * Under high memory pressure GFP_NOWAIT can fail,
 	 * in that case the emergency path is maintained.
 	 */
-	if (unlikely(!kfree_call_rcu_add_ptr_to_bulk(krcp, head, func))) {
+	if (is_vmalloc_addr((void *) head - (unsigned long) func) ||
+			!kfree_call_rcu_add_ptr_to_bulk(krcp, head, func)) {
 		head->func = func;
 		head->next = krcp->head;
 		krcp->head = head;
-- 
2.20.1