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Date: Sun, 01 Jun 2008 21:47:30 +0530
From: Abhishek Sagar <sagar.abhishek@...il.com>
To: rostedt@...dmis.org
CC: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/3] ftrace: prevent freeing of all failed updates
Prevent freeing of records which cause problems and correspond to function from
core kernel text. A new flag, FTRACE_FL_CONVERTED is used to mark a record
as "converted". All other records are patched lazily to NOPs. Failed records
now also remain on frace_hash table. Each invocation of ftrace_record_ip now
checks whether the traced function has ever been recorded (including past
failures) and doesn't re-record it again.
Signed-off-by: Abhishek Sagar <sagar.abhishek@...il.com>
---
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index b482fe8..fc4979a 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -49,6 +49,7 @@ enum {
FTRACE_FL_FILTER = (1 << 2),
FTRACE_FL_ENABLED = (1 << 3),
FTRACE_FL_NOTRACE = (1 << 4),
+ FTRACE_FL_CONVERTED = (1 << 5),
};
struct dyn_ftrace {
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 1843edc..33cee36 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -217,6 +217,12 @@ ftrace_add_hash(struct dyn_ftrace *node, unsigned long key)
hlist_add_head_rcu(&node->node, &ftrace_hash[key]);
}
+/* called from kstop_machine */
+static inline void ftrace_del_hash(struct dyn_ftrace *node)
+{
+ hlist_del(&node->node);
+}
+
static void ftrace_free_rec(struct dyn_ftrace *rec)
{
/* no locking, only called from kstop_machine */
@@ -333,12 +339,11 @@ ftrace_record_ip(unsigned long ip)
#define FTRACE_ADDR ((long)(ftrace_caller))
#define MCOUNT_ADDR ((long)(mcount))
-static void
+static int
__ftrace_replace_code(struct dyn_ftrace *rec,
unsigned char *old, unsigned char *new, int enable)
{
unsigned long ip, fl;
- int failed;
ip = rec->ip;
@@ -365,7 +370,7 @@ __ftrace_replace_code(struct dyn_ftrace *rec,
if ((fl == (FTRACE_FL_FILTER | FTRACE_FL_ENABLED)) ||
(fl == 0) || (rec->flags & FTRACE_FL_NOTRACE))
- return;
+ return 0;
/*
* If it is enabled disable it,
@@ -389,7 +394,7 @@ __ftrace_replace_code(struct dyn_ftrace *rec,
*/
fl = rec->flags & (FTRACE_FL_NOTRACE | FTRACE_FL_ENABLED);
if (fl == FTRACE_FL_NOTRACE)
- return;
+ return 0;
new = ftrace_call_replace(ip, FTRACE_ADDR);
} else
@@ -397,34 +402,24 @@ __ftrace_replace_code(struct dyn_ftrace *rec,
if (enable) {
if (rec->flags & FTRACE_FL_ENABLED)
- return;
+ return 0;
rec->flags |= FTRACE_FL_ENABLED;
} else {
if (!(rec->flags & FTRACE_FL_ENABLED))
- return;
+ return 0;
rec->flags &= ~FTRACE_FL_ENABLED;
}
}
- failed = ftrace_modify_code(ip, old, new);
- if (failed) {
- unsigned long key;
- /* It is possible that the function hasn't been converted yet */
- key = hash_long(ip, FTRACE_HASHBITS);
- if (!ftrace_ip_in_hash(ip, key)) {
- rec->flags |= FTRACE_FL_FAILED;
- ftrace_free_rec(rec);
- }
-
- }
+ return ftrace_modify_code(ip, old, new);
}
static void ftrace_replace_code(int enable)
{
+ int i, failed;
unsigned char *new = NULL, *old = NULL;
struct dyn_ftrace *rec;
struct ftrace_page *pg;
- int i;
if (enable)
old = ftrace_nop_replace();
@@ -439,7 +434,15 @@ static void ftrace_replace_code(int enable)
if (rec->flags & FTRACE_FL_FAILED)
continue;
- __ftrace_replace_code(rec, old, new, enable);
+ failed = __ftrace_replace_code(rec, old, new, enable);
+ if (failed && (rec->flags & FTRACE_FL_CONVERTED)) {
+ rec->flags |= FTRACE_FL_FAILED;
+ if ((system_state == SYSTEM_BOOTING) ||
+ !kernel_text_address(rec->ip)) {
+ ftrace_del_hash(rec);
+ ftrace_free_rec(rec);
+ }
+ }
}
}
}
@@ -468,7 +471,6 @@ ftrace_code_disable(struct dyn_ftrace *rec)
failed = ftrace_modify_code(ip, call, nop);
if (failed) {
rec->flags |= FTRACE_FL_FAILED;
- ftrace_free_rec(rec);
return 0;
}
return 1;
@@ -596,8 +598,7 @@ unsigned long ftrace_update_tot_cnt;
static int __ftrace_update_code(void *ignore)
{
struct dyn_ftrace *p;
- struct hlist_head head;
- struct hlist_node *t;
+ struct hlist_node *t, *n;
int save_ftrace_enabled;
cycle_t start, stop;
int i;
@@ -611,18 +612,33 @@ static int __ftrace_update_code(void *ignore)
/* No locks needed, the machine is stopped! */
for (i = 0; i < FTRACE_HASHSIZE; i++) {
- if (hlist_empty(&ftrace_hash[i]))
- continue;
+ /* all CPUS are stopped, we are safe to modify code */
+ hlist_for_each_entry_safe(p, t, n, &ftrace_hash[i], node) {
+ /* Skip over failed records which have not been
+ * freed. */
+ if (p->flags & FTRACE_FL_FAILED)
+ continue;
- head = ftrace_hash[i];
- INIT_HLIST_HEAD(&ftrace_hash[i]);
+ /* Unconverted records are always at the head of the
+ * hash bucket. Once we encounter a converted record,
+ * simply skip over to the next bucket. Saves ftraced
+ * some processor cycles (ftrace does its bid for
+ * global warming :-p ). */
+ if (p->flags & (FTRACE_FL_CONVERTED))
+ break;
- /* all CPUS are stopped, we are safe to modify code */
- hlist_for_each_entry(p, t, &head, node) {
- if (ftrace_code_disable(p))
+ if (ftrace_code_disable(p)) {
+ p->flags |= FTRACE_FL_CONVERTED;
ftrace_update_cnt++;
- }
+ } else {
+ if ((system_state == SYSTEM_BOOTING) ||
+ !kernel_text_address(p->ip)) {
+ ftrace_del_hash(p);
+ ftrace_free_rec(p);
+ }
+ }
+ }
}
stop = ftrace_now(raw_smp_processor_id());
--
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