Commit 66150d0d authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Alexei Starovoitov
Browse files

bpf, lpm: Make locking RT friendly 



The LPM trie map cannot be used in contexts like perf, kprobes and tracing
as this map type dynamically allocates memory.

The memory allocation happens with a raw spinlock held which is a truly
spinning lock on a PREEMPT RT enabled kernel which disables preemption and
interrupts.

As RT does not allow memory allocation from such a section for various
reasons, convert the raw spinlock to a regular spinlock.

On a RT enabled kernel these locks are substituted by 'sleeping' spinlocks
which provide the proper protection but keep the code preemptible.

On a non-RT kernel regular spinlocks map to raw spinlocks, i.e. this does
not cause any functional change.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200224145644.602129531@linutronix.de
parent 7f805d17

kernel/bpf/lpm_trie.c

+6 −6
Original line number Diff line number Diff line
@@ -34,7 +34,7 @@ struct lpm_trie { 
	size_t				n_entries;

	size_t				max_prefixlen;

	size_t				data_size;

	raw_spinlock_t			lock;

	spinlock_t			lock;

};



/* This trie implements a longest prefix match algorithm that can be used to
@@ -315,7 +315,7 @@ static int trie_update_elem(struct bpf_map *map, 
	if (key->prefixlen > trie->max_prefixlen)

		return -EINVAL;



	raw_spin_lock_irqsave(&trie->lock, irq_flags);

	spin_lock_irqsave(&trie->lock, irq_flags);



	/* Allocate and fill a new node */
@@ -422,7 +422,7 @@ out: 
		kfree(im_node);

	}



	raw_spin_unlock_irqrestore(&trie->lock, irq_flags);

	spin_unlock_irqrestore(&trie->lock, irq_flags);



	return ret;

}
@@ -442,7 +442,7 @@ static int trie_delete_elem(struct bpf_map *map, void *_key) 
	if (key->prefixlen > trie->max_prefixlen)

		return -EINVAL;



	raw_spin_lock_irqsave(&trie->lock, irq_flags);

	spin_lock_irqsave(&trie->lock, irq_flags);



	/* Walk the tree looking for an exact key/length match and keeping

	 * track of the path we traverse.  We will need to know the node
@@ -518,7 +518,7 @@ static int trie_delete_elem(struct bpf_map *map, void *_key) 
	kfree_rcu(node, rcu);



out:

	raw_spin_unlock_irqrestore(&trie->lock, irq_flags);

	spin_unlock_irqrestore(&trie->lock, irq_flags);



	return ret;

}
@@ -575,7 +575,7 @@ static struct bpf_map *trie_alloc(union bpf_attr *attr) 
	if (ret)

		goto out_err;



	raw_spin_lock_init(&trie->lock);

	spin_lock_init(&trie->lock);



	return &trie->map;

out_err:

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