ksym_tracer: Rewrite ksym_trace_filter_read()

Reading ksym_trace_filter gave me some arbitrary characters,
when it should show nothing. It's because buf is not initialized
when there's no filter.

Also reduce stack usage by about 512 bytes.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: "K.Prasad" <prasad@linux.vnet.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A52E2B4.6030706@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 18 insertions, 11 deletions

diff --git a/kernel/trace/trace_ksym.c b/kernel/trace/trace_ksym.c
index 085ff055fdfa..b6710d31bdf0 100644
--- a/kernel/trace/trace_ksym.c
+++ b/kernel/trace/trace_ksym.c
@@ -35,7 +35,6 @@
 #define KSYM_TRACER_MAX HBP_NUM
 
 #define KSYM_TRACER_OP_LEN 3 /* rw- */
-#define KSYM_FILTER_ENTRY_LEN (KSYM_NAME_LEN + KSYM_TRACER_OP_LEN + 1)
 
 struct trace_ksym {
         struct hw_breakpoint    *ksym_hbp;
@@ -230,25 +229,33 @@ static ssize_t ksym_trace_filter_read(struct file *filp, char __user *ubuf,
 {
         struct trace_ksym *entry;
         struct hlist_node *node;
-        char buf[KSYM_FILTER_ENTRY_LEN * KSYM_TRACER_MAX];
-        ssize_t ret, cnt = 0;
+        struct trace_seq *s;
+        ssize_t cnt = 0;
+        int ret;
+
+        s = kmalloc(sizeof(*s), GFP_KERNEL);
+        if (!s)
+                return -ENOMEM;
+        trace_seq_init(s);
 
         mutex_lock(&ksym_tracer_mutex);
 
         hlist_for_each_entry(entry, node, &ksym_filter_head, ksym_hlist) {
-                cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt, "%s:",
-                                entry->ksym_hbp->info.name);
+                ret = trace_seq_printf(s, "%s:", entry->ksym_hbp->info.name);
                 if (entry->ksym_hbp->info.type == HW_BREAKPOINT_WRITE)
-                        cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt,
-                                                                "-w-\n");
+                        ret = trace_seq_puts(s, "-w-\n");
                 else if (entry->ksym_hbp->info.type == HW_BREAKPOINT_RW)
-                        cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt,
-                                                                "rw-\n");
+                        ret = trace_seq_puts(s, "rw-\n");
+                WARN_ON_ONCE(!ret);
         }
-        ret = simple_read_from_buffer(ubuf, count, ppos, buf, strlen(buf));
+
+        cnt = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len);
+
         mutex_unlock(&ksym_tracer_mutex);
 
-        return ret;
+        kfree(s);
+
+        return cnt;
 }
 
 static ssize_t ksym_trace_filter_write(struct file *file,