ftrace: avoid modifying kprobe'd records

Avoid modifying the mcount call-site if there is a kprobe installed on it.
These records are not marked as failed however. This allowed the filter
rules on them to remain up-to-date. Whenever the kprobe on the corresponding
record is removed, the record gets updated as normal.

Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 31 insertions, 4 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index d1238163155f..85e841335417 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -21,6 +21,7 @@
 #include <linux/hardirq.h>
 #include <linux/kthread.h>
 #include <linux/uaccess.h>
+#include <linux/kprobes.h>
 #include <linux/ftrace.h>
 #include <linux/sysctl.h>
 #include <linux/ctype.h>
@@ -500,6 +501,10 @@ static void ftrace_replace_code(int enable)
                         if (rec->flags & FTRACE_FL_FAILED)
                                 continue;
 
+                        /* ignore updates to this record's mcount site */
+                        if (get_kprobe((void *)rec->ip))
+                                continue;
+
                         failed = __ftrace_replace_code(rec, old, new, enable);
                         if (failed && (rec->flags & FTRACE_FL_CONVERTED)) {
                                 rec->flags |= FTRACE_FL_FAILED;
@@ -692,11 +697,11 @@ unsigned long		ftrace_update_tot_cnt;
 
 static int __ftrace_update_code(void *ignore)
 {
+        int i, save_ftrace_enabled;
+        cycle_t start, stop;
         struct dyn_ftrace *p;
         struct hlist_node *t, *n;
-        int save_ftrace_enabled;
-        cycle_t start, stop;
-        int i;
+        struct hlist_head *head, temp_list;
 
         /* Don't be recording funcs now */
         ftrace_record_suspend++;
@@ -708,8 +713,11 @@ static int __ftrace_update_code(void *ignore)
 
         /* No locks needed, the machine is stopped! */
         for (i = 0; i < FTRACE_HASHSIZE; i++) {
+                INIT_HLIST_HEAD(&temp_list);
+                head = &ftrace_hash[i];
+
                 /* all CPUS are stopped, we are safe to modify code */
-                hlist_for_each_entry_safe(p, t, n, &ftrace_hash[i], node) {
+                hlist_for_each_entry_safe(p, t, n, head, node) {
                         /* Skip over failed records which have not been
                          * freed. */
                         if (p->flags & FTRACE_FL_FAILED)
@@ -723,6 +731,19 @@ static int __ftrace_update_code(void *ignore)
                         if (p->flags & (FTRACE_FL_CONVERTED))
                                 break;
 
+                        /* Ignore updates to this record's mcount site.
+                         * Reintroduce this record at the head of this
+                         * bucket to attempt to "convert" it again if
+                         * the kprobe on it is unregistered before the
+                         * next run. */
+                        if (get_kprobe((void *)p->ip)) {
+                                ftrace_del_hash(p);
+                                INIT_HLIST_NODE(&p->node);
+                                hlist_add_head(&p->node, &temp_list);
+                                continue;
+                        }
+
+                        /* convert record (i.e, patch mcount-call with NOP) */
                         if (ftrace_code_disable(p)) {
                                 p->flags |= FTRACE_FL_CONVERTED;
                                 ftrace_update_cnt++;
@@ -734,6 +755,12 @@ static int __ftrace_update_code(void *ignore)
                                 }
                         }
                 }
+
+                hlist_for_each_entry_safe(p, t, n, &temp_list, node) {
+                        hlist_del(&p->node);
+                        INIT_HLIST_NODE(&p->node);
+                        hlist_add_head(&p->node, head);
+                }
         }
 
         stop = ftrace_now(raw_smp_processor_id());