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Commit 99815f50 authored by Vlad Buslov's avatar Vlad Buslov Committed by David S. Miller
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net: sched: flower: don't call synchronize_rcu() on mask creation 



Current flower mask creating code assumes that temporary mask that is used
when inserting new filter is stack allocated. To prevent race condition
with data patch synchronize_rcu() is called every time fl_create_new_mask()
replaces temporary stack allocated mask. As reported by Jiri, this
increases runtime of creating 20000 flower classifiers from 4 seconds to
163 seconds. However, this design is no longer necessary since temporary
mask was converted to be dynamically allocated by commit 2cddd201
("net/sched: cls_flower: allocate mask dynamically in fl_change()").

Remove synchronize_rcu() calls from mask creation code. Instead, refactor
fl_change() to always deallocate temporary mask with rcu grace period.

Fixes: 195c234d ("net: sched: flower: handle concurrent mask insertion")
Reported-by: default avatarJiri Pirko <jiri@mellanox.com>
Signed-off-by: default avatarVlad Buslov <vladbu@mellanox.com>
Tested-by: default avatarJiri Pirko <jiri@mellanox.com>
Acked-by: default avatarJiri Pirko <jiri@mellanox.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f0c03ee0

net/sched/cls_flower.c

+18 −16
Original line number Diff line number Diff line
@@ -320,10 +320,13 @@ static int fl_init(struct tcf_proto *tp) 
	return rhashtable_init(&head->ht, &mask_ht_params);

}



static void fl_mask_free(struct fl_flow_mask *mask)

static void fl_mask_free(struct fl_flow_mask *mask, bool mask_init_done)

{

	/* temporary masks don't have their filters list and ht initialized */

	if (mask_init_done) {

		WARN_ON(!list_empty(&mask->filters));

		rhashtable_destroy(&mask->ht);

	}

	kfree(mask);

}
@@ -332,7 +335,15 @@ static void fl_mask_free_work(struct work_struct *work) 
	struct fl_flow_mask *mask = container_of(to_rcu_work(work),

						 struct fl_flow_mask, rwork);



	fl_mask_free(mask);

	fl_mask_free(mask, true);

}



static void fl_uninit_mask_free_work(struct work_struct *work)

{

	struct fl_flow_mask *mask = container_of(to_rcu_work(work),

						 struct fl_flow_mask, rwork);



	fl_mask_free(mask, false);

}



static bool fl_mask_put(struct cls_fl_head *head, struct fl_flow_mask *mask)
@@ -1346,9 +1357,6 @@ static struct fl_flow_mask *fl_create_new_mask(struct cls_fl_head *head, 
	if (err)

		goto errout_destroy;



	/* Wait until any potential concurrent users of mask are finished */

	synchronize_rcu();



	spin_lock(&head->masks_lock);

	list_add_tail_rcu(&newmask->list, &head->masks);

	spin_unlock(&head->masks_lock);
@@ -1375,11 +1383,7 @@ static int fl_check_assign_mask(struct cls_fl_head *head, 


	/* Insert mask as temporary node to prevent concurrent creation of mask

	 * with same key. Any concurrent lookups with same key will return

	 * -EAGAIN because mask's refcnt is zero. It is safe to insert

	 * stack-allocated 'mask' to masks hash table because we call

	 * synchronize_rcu() before returning from this function (either in case

	 * of error or after replacing it with heap-allocated mask in

	 * fl_create_new_mask()).

	 * -EAGAIN because mask's refcnt is zero.

	 */

	fnew->mask = rhashtable_lookup_get_insert_fast(&head->ht,

						       &mask->ht_node,
@@ -1414,8 +1418,6 @@ static int fl_check_assign_mask(struct cls_fl_head *head, 
errout_cleanup:

	rhashtable_remove_fast(&head->ht, &mask->ht_node,

			       mask_ht_params);

	/* Wait until any potential concurrent users of mask are finished */

	synchronize_rcu();

	return ret;

}
@@ -1644,7 +1646,7 @@ static int fl_change(struct net *net, struct sk_buff *in_skb, 
	*arg = fnew;



	kfree(tb);

	kfree(mask);

	tcf_queue_work(&mask->rwork, fl_uninit_mask_free_work);

	return 0;



errout_ht:
@@ -1664,7 +1666,7 @@ static int fl_change(struct net *net, struct sk_buff *in_skb, 
errout_tb:

	kfree(tb);

errout_mask_alloc:

	kfree(mask);

	tcf_queue_work(&mask->rwork, fl_uninit_mask_free_work);

errout_fold:

	if (fold)

		__fl_put(fold);