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Subject[PATCH] ftrace: safe traversal of ftrace_hash hlist
Hi Steven,

I noticed that concurrent instances of ftrace_record_ip() have a race between ftrace_hash list traversal during ftrace_ip_in_hash() (before acquiring ftrace_shutdown_lock) and ftrace_add_hash().If it's so then this should fix it.

Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
---
Accommodate traversal of ftrace_hash hlist with concurrent insertions.

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 89bd9a6..bfba25c 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -201,7 +201,7 @@ ftrace_ip_in_hash(unsigned long ip, unsigned long key)
struct hlist_node *t;
int found = 0;

- hlist_for_each_entry(p, t, &ftrace_hash[key], node) {
+ hlist_for_each_entry_rcu(p, t, &ftrace_hash[key], node) {
if (p->ip == ip) {
found = 1;
break;
@@ -214,7 +214,7 @@ ftrace_ip_in_hash(unsigned long ip, unsigned long key)
static inline void
ftrace_add_hash(struct dyn_ftrace *node, unsigned long key)
{
- hlist_add_head(&node->node, &ftrace_hash[key]);
+ hlist_add_head_rcu(&node->node, &ftrace_hash[key]);
}

static void ftrace_free_rec(struct dyn_ftrace *rec)

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