linux-kernel - [PATCH 4/4] mm: Do periodic rescheduling when freeing objects in kmem_free_up

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Date:   Thu, 21 Mar 2019 17:45:12 -0400
From:   Waiman Long <longman@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        selinux@...r.kernel.org, Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH 4/4] mm: Do periodic rescheduling when freeing objects in kmem_free_up_q()

If the freeing queue has many objects, freeing all of them consecutively
may cause soft lockup especially on a debug kernel. So kmem_free_up_q()
is modified to call cond_resched() if running in the process context.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 mm/slab_common.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index dba20b4208f1..633a1d0f6d20 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1622,11 +1622,14 @@ EXPORT_SYMBOL_GPL(kmem_free_q_add);
  * kmem_free_up_q - free all the objects in the freeing queue
  * @head: freeing queue head
  *
- * Free all the objects in the freeing queue.
+ * Free all the objects in the freeing queue. The caller cannot hold any
+ * non-sleeping locks.
  */
 void kmem_free_up_q(struct kmem_free_q_head *head)
 {
 	struct kmem_free_q_node *node, *next;
+	bool do_resched = !in_irq();
+	int cnt = 0;
 
 	for (node = head->first; node; node = next) {
 		next = node->next;
@@ -1634,6 +1637,12 @@ void kmem_free_up_q(struct kmem_free_q_head *head)
 			kmem_cache_free(node->cachep, node);
 		else
 			kfree(node);
+		/*
+		 * Call cond_resched() every 256 objects freed when in
+		 * process context.
+		 */
+		if (do_resched && !(++cnt & 0xff))
+			cond_resched();
 	}
 }
 EXPORT_SYMBOL_GPL(kmem_free_up_q);
-- 
2.18.1