[PATCH 3.2 182/185] ftrace: Create ftrace_hash_empty() helper routine

Ben Hutchings
2013-12-29T02:08:44Z

From: Steven Rostedt <srostedt@redhat.com>

commit 06a51d9307380c78bb5c92e68fc80ad2c7d7f890 upstream.

There are two types of hashes in the ftrace_ops; one type
is the filter_hash and the other is the notrace_hash. Either
one may be null, meaning it has no elements. But when elements
are added, the hash is allocated.

Throughout the code, a check needs to be made to see if a hash
exists or the hash has elements, but the check if the hash exists
is usually missing causing the possible "NULL pointer dereference bug".

Add a helper routine called "ftrace_hash_empty()" that returns
true if the hash doesn't exist or its count is zero. As they mean
the same thing.

Last-bug-reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/trace/ftrace.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1017,6 +1017,11 @@ static struct ftrace_page *ftrace_pages;

static struct dyn_ftrace *ftrace_free_records;

+static bool ftrace_hash_empty(struct ftrace_hash *hash)
+{
+ return !hash || !hash->count;
+}
+
static struct ftrace_func_entry *
ftrace_lookup_ip(struct ftrace_hash *hash, unsigned long ip)
{
@@ -1025,7 +1030,7 @@ ftrace_lookup_ip(struct ftrace_hash *has
struct hlist_head *hhd;
struct hlist_node *n;

- if (!hash->count)
+ if (ftrace_hash_empty(hash))
return NULL;

if (hash->size_bits > 0)
@@ -1169,7 +1174,7 @@ alloc_and_copy_ftrace_hash(int size_bits
return NULL;

/* Empty hash? */
- if (!hash || !hash->count)
+ if (ftrace_hash_empty(hash))
return new_hash;

size = 1 << hash->size_bits;
@@ -1294,9 +1299,9 @@ ftrace_ops_test(struct ftrace_ops *ops,
filter_hash = rcu_dereference_raw(ops->filter_hash);
notrace_hash = rcu_dereference_raw(ops->notrace_hash);

- if ((!filter_hash || !filter_hash->count ||
+ if ((ftrace_hash_empty(filter_hash) ||
ftrace_lookup_ip(filter_hash, ip)) &&
- (!notrace_hash || !notrace_hash->count ||
+ (ftrace_hash_empty(notrace_hash) ||
!ftrace_lookup_ip(notrace_hash, ip)))
ret = 1;
else
@@ -1348,7 +1353,7 @@ static void __ftrace_hash_rec_update(str
if (filter_hash) {
hash = ops->filter_hash;
other_hash = ops->notrace_hash;
- if (!hash || !hash->count)
+ if (ftrace_hash_empty(hash))
all = 1;
} else {
inc = !inc;
@@ -1358,7 +1363,7 @@ static void __ftrace_hash_rec_update(str
* If the notrace hash has no items,
* then there's nothing to do.
*/
- if (!hash || !hash->count)
+ if (ftrace_hash_empty(hash))
return;
}

@@ -1375,8 +1380,8 @@ static void __ftrace_hash_rec_update(str
if (!other_hash || !ftrace_lookup_ip(other_hash, rec->ip))
match = 1;
} else {
- in_hash = hash && !!ftrace_lookup_ip(hash, rec->ip);
- in_other_hash = other_hash && !!ftrace_lookup_ip(other_hash, rec->ip);
+ in_hash = !!ftrace_lookup_ip(hash, rec->ip);
+ in_other_hash = !!ftrace_lookup_ip(other_hash, rec->ip);

/*
*
@@ -1384,7 +1389,7 @@ static void __ftrace_hash_rec_update(str
if (filter_hash && in_hash && !in_other_hash)
match = 1;
else if (!filter_hash && in_hash &&
- (in_other_hash || !other_hash->count))
+ (in_other_hash || ftrace_hash_empty(other_hash)))
match = 1;
}
if (!match)
@@ -1799,7 +1804,7 @@ static int ops_traces_mod(struct ftrace_
struct ftrace_hash *hash;

hash = ops->filter_hash;
- return !!(!hash || !hash->count);
+ return ftrace_hash_empty(hash);
}

static int ftrace_update_code(struct module *mod)
@@ -2112,7 +2117,8 @@ static void *t_start(struct seq_file *m,
* off, we can short cut and just print out that all
* functions are enabled.
*/
- if (iter->flags & FTRACE_ITER_FILTER && !ops->filter_hash->count) {
+ if (iter->flags & FTRACE_ITER_FILTER &&
+ ftrace_hash_empty(ops->filter_hash)) {
if (*pos > 0)
return t_hash_start(m, pos);
iter->flags |= FTRACE_ITER_PRINTALL;