From: Steven Rostedt (VMware) Date: Fri, 30 Aug 2019 20:30:01 +0000 (-0400) Subject: ftrace: Check for empty hash and comment the race with registering probes X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=04497185f67dd571121e1a44b252229493406558;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git ftrace: Check for empty hash and comment the race with registering probes 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) Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index b6bdc765d847..10b3e3b22af6 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -3185,7 +3185,11 @@ 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; @@ -4384,6 +4388,10 @@ 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;