From: "Steven Rostedt (VMware)" rostedt@goodmis.org

The race between adding a function probe and reading the probes that exist is very subtle. It needs a comment. Also, the issue can also happen if the probe has has the EMPTY_HASH as its func_hash.

Cc: stable@vger.kernel.org Fixes: 7b60f3d876156 ("ftrace: Dynamically create the probe ftrace_ops for the trace_array") Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org --- kernel/trace/ftrace.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 80beed2cf0da..6200a6fe10e3 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -3096,7 +3096,11 @@ t_probe_next(struct seq_file *m, loff_t *pos)

hash = iter->probe->ops.func_hash->filter_hash;

- if (!hash) + /* + * A probe being registered may temporarily have an empty hash + * and it's at the end of the func_probes list. + */ + if (!hash || hash == EMPTY_HASH) return NULL;

size = 1 << hash->size_bits; @@ -4324,6 +4328,10 @@ register_ftrace_function_probe(char *glob, struct trace_array *tr,

mutex_unlock(&ftrace_lock);

+ /* + * Note, there's a small window here that the func_hash->filter_hash + * may be NULL or empty. Need to be carefule when reading the loop. + */ mutex_lock(&probe->ops.func_hash->regex_lock);

orig_hash = &probe->ops.func_hash->filter_hash;