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>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200224145644.602129531@linutronix.de

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index 56e6c75d354d9027622f78fe5de5d2e4bb982640..3b3c420bc8ed8eb1b5713280509070c774497d8f 100644 (file)
--- 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_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: