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Subject[RFC patch 18/19] 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: Thomas Gleixner <tglx@linutronix.de>
---
kernel/bpf/lpm_trie.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -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_m
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 @@ static int trie_update_elem(struct bpf_m
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_m
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_m
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
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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