ftrace: Free hash with call_rcu_sched()

When a hash is modified and might be in use, we need to perform
a schedule RCU operation on it, as the hashes will soon be used
directly in the function tracer callback.

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index dcce0bf9c84dd85ff1ed27a85640c39376bdd916..92b6fdf49ae52f7e3d0572dcd4b61948f1cd4e7f 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -913,6 +913,7 @@ struct ftrace_hash {
        unsigned long           size_bits;
        struct hlist_head       *buckets;
        unsigned long           count;
+       struct rcu_head         rcu;
 };
 
 /*
@@ -1058,6 +1059,21 @@ static void free_ftrace_hash(struct ftrace_hash *hash)
        kfree(hash);
 }
 
+static void __free_ftrace_hash_rcu(struct rcu_head *rcu)
+{
+       struct ftrace_hash *hash;
+
+       hash = container_of(rcu, struct ftrace_hash, rcu);
+       free_ftrace_hash(hash);
+}
+
+static void free_ftrace_hash_rcu(struct ftrace_hash *hash)
+{
+       if (!hash || hash == EMPTY_HASH)
+               return;
+       call_rcu_sched(&hash->rcu, __free_ftrace_hash_rcu);
+}
+
 static struct ftrace_hash *alloc_ftrace_hash(int size_bits)
 {
        struct ftrace_hash *hash;
@@ -1122,7 +1138,8 @@ ftrace_hash_move(struct ftrace_hash **dst, struct ftrace_hash *src)
        struct ftrace_func_entry *entry;
        struct hlist_node *tp, *tn;
        struct hlist_head *hhd;
-       struct ftrace_hash *hash = *dst;
+       struct ftrace_hash *old_hash;
+       struct ftrace_hash *new_hash;
        unsigned long key;
        int size = src->count;
        int bits = 0;
@@ -1133,13 +1150,11 @@ ftrace_hash_move(struct ftrace_hash **dst, struct ftrace_hash *src)
         * the empty_hash.
         */
        if (!src->count) {
-               free_ftrace_hash(*dst);
-               *dst = EMPTY_HASH;
+               free_ftrace_hash_rcu(*dst);
+               rcu_assign_pointer(*dst, EMPTY_HASH);
                return 0;
        }
 
-       ftrace_hash_clear(hash);
-
        /*
         * Make the hash size about 1/2 the # found
         */
@@ -1150,27 +1165,9 @@ ftrace_hash_move(struct ftrace_hash **dst, struct ftrace_hash *src)
        if (bits > FTRACE_HASH_MAX_BITS)
                bits = FTRACE_HASH_MAX_BITS;
 
-       /* We can't modify the empty_hash */
-       if (hash == EMPTY_HASH) {
-               /* Create a new hash */
-               *dst = alloc_ftrace_hash(bits);
-               if (!*dst) {
-                       *dst = EMPTY_HASH;
-                       return -ENOMEM;
-               }
-               hash = *dst;
-       } else {
-               size = 1 << bits;
-
-               /* Use the old hash, but create new buckets */
-               hhd = kzalloc(sizeof(*hhd) * size, GFP_KERNEL);
-               if (!hhd)
-                       return -ENOMEM;
-
-               kfree(hash->buckets);
-               hash->buckets = hhd;
-               hash->size_bits = bits;
-       }
+       new_hash = alloc_ftrace_hash(bits);
+       if (!new_hash)
+               return -ENOMEM;
 
        size = 1 << src->size_bits;
        for (i = 0; i < size; i++) {
@@ -1181,10 +1178,14 @@ ftrace_hash_move(struct ftrace_hash **dst, struct ftrace_hash *src)
                        else
                                key = 0;
                        remove_hash_entry(src, entry);
-                       __add_hash_entry(hash, entry);
+                       __add_hash_entry(new_hash, entry);
                }
        }
 
+       old_hash = *dst;
+       rcu_assign_pointer(*dst, new_hash);
+       free_ftrace_hash_rcu(old_hash);
+
        return 0;
 }