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>

1 files changed, 28 insertions, 27 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index dcce0bf9c84d..92b6fdf49ae5 100644
--- 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;
 }