ksym_tracer: Fix race when incrementing count

We are under rcu read section but not holding the write lock, so
count++ is not atomic. Use atomic64_t instead.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4B3AF1EC.9010608@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/trace/trace_ksym.c b/kernel/trace/trace_ksym.c
index 160a8d8b37a2..67d79f709fc5 100644
--- a/kernel/trace/trace_ksym.c
+++ b/kernel/trace/trace_ksym.c
@@ -32,6 +32,8 @@
 #include <linux/hw_breakpoint.h>
 #include <asm/hw_breakpoint.h>
 
+#include <asm/atomic.h>
+
 /*
  * For now, let us restrict the no. of symbols traced simultaneously to number
  * of available hardware breakpoint registers.
@@ -44,7 +46,7 @@ struct trace_ksym {
         struct perf_event       **ksym_hbp;
         struct perf_event_attr  attr;
 #ifdef CONFIG_PROFILE_KSYM_TRACER
-        unsigned long           counter;
+        atomic64_t              counter;
 #endif
         struct hlist_node       ksym_hlist;
 };
@@ -69,9 +71,8 @@ void ksym_collect_stats(unsigned long hbp_hit_addr)
 
         rcu_read_lock();
         hlist_for_each_entry_rcu(entry, node, &ksym_filter_head, ksym_hlist) {
-                if ((entry->attr.bp_addr == hbp_hit_addr) &&
-                    (entry->counter <= MAX_UL_INT)) {
-                        entry->counter++;
+                if (entry->attr.bp_addr == hbp_hit_addr) {
+                        atomic64_inc(&entry->counter);
                         break;
                 }
         }
@@ -501,7 +502,8 @@ static int ksym_tracer_stat_show(struct seq_file *m, void *v)
                 seq_printf(m, "  %-36s", fn_name);
         else
                 seq_printf(m, "  %-36s", "<NA>");
-        seq_printf(m, " %15lu\n", entry->counter);
+        seq_printf(m, " %15llu\n",
+                   (unsigned long long)atomic64_read(&entry->counter));
 
         return 0;
 }