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SubjectRe: [PATCH 5/5] tracing: reset iterator in t_start()
Li Zefan wrote:
> The iterator is m->private, but it's not reset to trace_types in
> t_start(). If the output is larger than PAGE_SIZE and t_start()
> is called the 2nd time, things will go wrong.
>
> [ Impact: fix output of current_tracer when it's larger than PAGE_SIZE ]
>
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
> kernel/trace/trace.c | 18 ++++--------------
> 1 files changed, 4 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 076fa6f..3bb3100 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2053,25 +2053,23 @@ static int tracing_open(struct inode *inode, struct file *file)
> static void *
> t_next(struct seq_file *m, void *v, loff_t *pos)
> {
> - struct tracer *t = m->private;
> + struct tracer *t = v;
>
> (*pos)++;
>
> if (t)
> t = t->next;
>
> - m->private = t;
> -
> return t;
> }
>
> static void *t_start(struct seq_file *m, loff_t *pos)
> {
> - struct tracer *t = m->private;
> + struct tracer *t;
> loff_t l = 0;
>
> mutex_lock(&trace_types_lock);
> - for (; t && l < *pos; t = t_next(m, t, &l))
> + for (t = trace_types; t && l < *pos; t = t_next(m, t, &l))
> ;
>
> return t;
> @@ -2107,18 +2105,10 @@ static struct seq_operations show_traces_seq_ops = {
>
> static int show_traces_open(struct inode *inode, struct file *file)
> {
> - int ret;
> -
> if (tracing_disabled)
> return -ENODEV;
>
> - ret = seq_open(file, &show_traces_seq_ops);
> - if (!ret) {
> - struct seq_file *m = file->private_data;
> - m->private = trace_types;
> - }
> -
> - return ret;
> + return seq_open(file, &show_traces_seq_ops);
> }
>
> static ssize_t
Another version:
Since we have saved current (struct tracer *) in m->private in .next, in .start,
we don't need to call .next to find the one that should be printed in 2nd or nth
time.

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index cae34c6..02cdccc 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2055,8 +2055,6 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
{
struct tracer *t = m->private;

- (*pos)++;
-
if (t)
t = t->next;

@@ -2068,11 +2066,8 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
static void *t_start(struct seq_file *m, loff_t *pos)
{
struct tracer *t = m->private;
- loff_t l = 0;

mutex_lock(&trace_types_lock);
- for (; t && l < *pos; t = t_next(m, t, &l))
- ;

return t;
}

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