From: Steven Rostedt (VMware) rostedt@goodmis.org
commit 372e0d01da71c84dcecf7028598a33813b0d5256 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/trace/ftrace.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
--- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -3096,7 +3096,11 @@ t_probe_next(struct seq_file *m, loff_t
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 *glo
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;