On Thu, 4 Jul 2019 20:04:41 +0530
"Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> kernel/trace/ftrace.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 7b037295a1f1..0791eafb693d 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -3093,6 +3093,10 @@ t_probe_next(struct seq_file *m, loff_t *pos)
> hnd = &iter->probe_entry->hlist;
>
> hash = iter->probe->ops.func_hash->filter_hash;
> +
> + if (!hash)
> + return NULL;
> +
> size = 1 << hash->size_bits;
>
> retry:
OK, I added this, but I'm also adding this on top:
-- Steve
>From 372e0d01da71c84dcecf7028598a33813b0d5256 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rost...@goodmis.org>
Date: Fri, 30 Aug 2019 16:30:01 -0400
Subject: [PATCH] ftrace: Check for empty hash and comment the race with
registering probes
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: sta...@vger.kernel.org
Fixes: 7b60f3d876156 ("ftrace: Dynamically create the probe ftrace_ops for the
trace_array")
Signed-off-by: Steven Rostedt (VMware) <rost...@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;
--
2.20.1
