[PATCH V2 1/2] ftrace: Make saved_cmdlines use seq_read

Yoshihiro YUNOMAE
2014-02-20T08:44:37Z

Current tracing_saved_cmdlines_read() implementation is naive;
simply allocate a big buffer, construct output data on the
buffer for each read operation, and then copy a portion of
the buffer to the user space buffer. This can cause a couple of
issues such as a slow memory allocation, high cpu usage, and a
corruption of the output data.

To address these issues, make saved_cmdlines use seq_read.

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-kernel@vger.kernel.org
---
kernel/trace/trace.c | 89 ++++++++++++++++++++++++++++++--------------------
1 file changed, 54 insertions(+), 35 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 815c878..b97648aa 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3638,55 +3638,74 @@ static const struct file_operations tracing_readme_fops = {
.llseek = generic_file_llseek,
};

-static ssize_t
-tracing_saved_cmdlines_read(struct file *file, char __user *ubuf,
- size_t cnt, loff_t *ppos)
+static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
{
- char *buf_comm;
- char *file_buf;
- char *buf;
- int len = 0;
- int pid;
- int i;
+ unsigned int *ptr = v;

- file_buf = kmalloc(SAVED_CMDLINES*(16+TASK_COMM_LEN), GFP_KERNEL);
- if (!file_buf)
- return -ENOMEM;
+ if (*pos || m->count)
+ ptr++;

- buf_comm = kmalloc(TASK_COMM_LEN, GFP_KERNEL);
- if (!buf_comm) {
- kfree(file_buf);
- return -ENOMEM;
- }
+ (*pos)++;
+
+ for (; ptr < &map_cmdline_to_pid[SAVED_CMDLINES]; ptr++) {
+ if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
+ continue;

- buf = file_buf;
+ return ptr;
+ }

- for (i = 0; i < SAVED_CMDLINES; i++) {
- int r;
+ return NULL;
+}

- pid = map_cmdline_to_pid[i];
- if (pid == -1 || pid == NO_CMDLINE_MAP)
- continue;
+static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
+{
+ void *v;
+ loff_t l = 0;

- trace_find_cmdline(pid, buf_comm);
- r = sprintf(buf, "%d %s\n", pid, buf_comm);
- buf += r;
- len += r;
+ v = &map_cmdline_to_pid[0];
+ while (l <= *pos) {
+ v = saved_cmdlines_next(m, v, &l);
+ if (!v)
+ return NULL;
}

- len = simple_read_from_buffer(ubuf, cnt, ppos,
- file_buf, len);
+ return v;
+}

- kfree(file_buf);
- kfree(buf_comm);
+static void saved_cmdlines_stop(struct seq_file *m, void *v)
+{
+}

- return len;
+static int saved_cmdlines_show(struct seq_file *m, void *v)
+{
+ char buf[TASK_COMM_LEN];
+ unsigned int *pid = v;
+
+ trace_find_cmdline(*pid, buf);
+ seq_printf(m, "%d %s\n", *pid, buf);
+ return 0;
+}
+
+static const struct seq_operations tracing_saved_cmdlines_seq_ops = {
+ .start = saved_cmdlines_start,
+ .next = saved_cmdlines_next,
+ .stop = saved_cmdlines_stop,
+ .show = saved_cmdlines_show,
+};
+
+static int tracing_saved_cmdlines_open(struct inode *inode, struct file *filp)
+{
+ if (tracing_disabled)
+ return -ENODEV;
+
+ return seq_open(filp, &tracing_saved_cmdlines_seq_ops);
}

static const struct file_operations tracing_saved_cmdlines_fops = {
- .open = tracing_open_generic,
- .read = tracing_saved_cmdlines_read,
- .llseek = generic_file_llseek,
+ .open = tracing_saved_cmdlines_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
};

static ssize_t