linux-kernel - [PATCH 3/4] ksym_tracer: Fix race when incrementing count

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Date:	Wed, 30 Dec 2009 14:23:40 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/4] 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@...fujitsu.com>
---
 kernel/trace/trace_ksym.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_ksym.c b/kernel/trace/trace_ksym.c
index 160a8d8..67d79f7 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;
 }
-- 
1.6.3

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