tracing: Change f_start() to take event_mutex and verify i_private != NULL
trace_format_open() and trace_format_seq_ops are racy, nothing protects ftrace_event_call from trace_remove_event_call(). Change f_start() to take event_mutex and verify i_private != NULL, change f_stop() to drop this lock. This fixes nothing, but now we can change debugfs_remove("format") callers to nullify ->i_private and fix the the problem. Note: the usage of event_mutex is sub-optimal but simple, we can change this later. Link: http://lkml.kernel.org/r/20130726172543.GA3622@redhat.com Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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@ -840,7 +840,7 @@ enum {
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static void *f_next(struct seq_file *m, void *v, loff_t *pos)
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{
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struct ftrace_event_call *call = m->private;
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struct ftrace_event_call *call = event_file_data(m->private);
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struct list_head *common_head = &ftrace_common_fields;
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struct list_head *head = trace_get_fields(call);
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struct list_head *node = v;
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@ -872,7 +872,7 @@ static void *f_next(struct seq_file *m, void *v, loff_t *pos)
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static int f_show(struct seq_file *m, void *v)
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{
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struct ftrace_event_call *call = m->private;
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struct ftrace_event_call *call = event_file_data(m->private);
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struct ftrace_event_field *field;
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const char *array_descriptor;
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@ -925,6 +925,11 @@ static void *f_start(struct seq_file *m, loff_t *pos)
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void *p = (void *)FORMAT_HEADER;
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loff_t l = 0;
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/* ->stop() is called even if ->start() fails */
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mutex_lock(&event_mutex);
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if (!event_file_data(m->private))
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return ERR_PTR(-ENODEV);
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while (l < *pos && p)
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p = f_next(m, p, &l);
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@ -933,6 +938,7 @@ static void *f_start(struct seq_file *m, loff_t *pos)
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static void f_stop(struct seq_file *m, void *p)
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{
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mutex_unlock(&event_mutex);
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}
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static const struct seq_operations trace_format_seq_ops = {
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@ -944,7 +950,6 @@ static const struct seq_operations trace_format_seq_ops = {
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static int trace_format_open(struct inode *inode, struct file *file)
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{
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struct ftrace_event_call *call = inode->i_private;
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struct seq_file *m;
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int ret;
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@ -953,7 +958,7 @@ static int trace_format_open(struct inode *inode, struct file *file)
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return ret;
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m = file->private_data;
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m->private = call;
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m->private = file;
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return 0;
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}
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