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Subject[RFC PATCH 6/4] tracing: Change f_start() to verify i_private under event_mutex
Finally change f_start() to take event_mutex and verify i_private,
f_stop() drops this lock. This closes the races with event_remove.

Note: the usage of event_mutex is sub-optimal but simple, we can
change this later.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/trace/trace_events.c | 17 +++++++++++++----
1 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 6c3e4e6..dc6c1ee 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -805,7 +805,8 @@ enum {

static void *f_next(struct seq_file *m, void *v, loff_t *pos)
{
- struct ftrace_event_call *call = m->private;
+ struct inode *inode = m->private;
+ struct ftrace_event_call *call = inode->i_private;
struct list_head *common_head = &ftrace_common_fields;
struct list_head *head = trace_get_fields(call);
struct list_head *node = v;
@@ -837,7 +838,8 @@ static void *f_next(struct seq_file *m, void *v, loff_t *pos)

static int f_show(struct seq_file *m, void *v)
{
- struct ftrace_event_call *call = m->private;
+ struct inode *inode = m->private;
+ struct ftrace_event_call *call = inode->i_private;
struct ftrace_event_field *field;
const char *array_descriptor;

@@ -887,9 +889,16 @@ static int f_show(struct seq_file *m, void *v)

static void *f_start(struct seq_file *m, loff_t *pos)
{
+ struct inode *inode = m->private;
void *p = (void *)FORMAT_HEADER;
loff_t l = 0;

+ mutex_lock(&event_mutex);
+ if (unlikely(!inode->i_private)) {
+ mutex_unlock(&event_mutex);
+ return ERR_PTR(-ENODEV);
+ }
+
while (p && l < *pos)
p = f_next(m, p, &l);

@@ -898,6 +907,7 @@ static void *f_start(struct seq_file *m, loff_t *pos)

static void f_stop(struct seq_file *m, void *p)
{
+ mutex_unlock(&event_mutex);
}

static const struct seq_operations trace_format_seq_ops = {
@@ -909,7 +919,6 @@ static const struct seq_operations trace_format_seq_ops = {

static int trace_format_open(struct inode *inode, struct file *file)
{
- struct ftrace_event_call *call = inode->i_private;
struct seq_file *m;
int ret;

@@ -918,7 +927,7 @@ static int trace_format_open(struct inode *inode, struct file *file)
return ret;

m = file->private_data;
- m->private = call;
+ m->private = inode;

return 0;
}
--
1.5.5.1



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