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SubjectRe: [PATCH 1/6] tracing: Turn event/id->i_private into call->event.type
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On Tue, 2013-07-23 at 22:59 +0200, Oleg Nesterov wrote:
> event_id_read() is racy, ftrace_event_call can be already freed
> by trace_remove_event_call() callers.
>
> Change event_create_dir() to pass "data = call->event.type", this
> is all event_id_read() needs. ftrace_event_id_fops no longer needs
> tracing_open_generic().
>
> We add the new helper, event_file_data(), to read ->i_private, it
> will have more users.
>
> Note: currently ACCESS_ONCE() and "id != 0" check are not needed,
> but we are going to change event_remove/rmdir to clear ->i_mutex.

We are changing i_mutex or i_private?

Anyway, this still looks too complex for the id. Just pass the id number
to the filp->private_data, and use that. It should never be cleared, and
as we are not using any pointers it will always return what the id
is/was.

Keep tracing_open_generic() and have:

event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t
*ppos)
{
int id = (int)(unsigned long)filp->private_data;
char buf[32];
int len;

if (*ppos)
return 0;

len = sprintf(buf, "%d\n", id);
return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
}

No need for accessing the inode->i_private.

-- Steve

>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> kernel/trace/trace_events.c | 17 ++++++++++++-----
> 1 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 76eed53..77990c4 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -409,6 +409,11 @@ static void put_system(struct ftrace_subsystem_dir *dir)
> mutex_unlock(&event_mutex);
> }
>
> +static void *event_file_data(struct file *filp)
> +{
> + return ACCESS_ONCE(file_inode(filp)->i_private);
> +}
> +
> /*
> * Open and update trace_array ref count.
> * Must have the current trace_array passed to it.
> @@ -946,14 +951,17 @@ static int trace_format_open(struct inode *inode, struct file *file)
> static ssize_t
> event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
> {
> - struct ftrace_event_call *call = filp->private_data;
> + int id = (long)event_file_data(filp);
> char buf[32];
> int len;
>
> if (*ppos)
> return 0;
>
> - len = sprintf(buf, "%d\n", call->event.type);
> + if (unlikely(!id))
> + return -ENODEV;
> +
> + len = sprintf(buf, "%d\n", id);
> return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
> }
>
> @@ -1240,7 +1248,6 @@ static const struct file_operations ftrace_event_format_fops = {
> };
>
> static const struct file_operations ftrace_event_id_fops = {
> - .open = tracing_open_generic,
> .read = event_id_read,
> .llseek = default_llseek,
> };
> @@ -1488,8 +1495,8 @@ event_create_dir(struct dentry *parent,
>
> #ifdef CONFIG_PERF_EVENTS
> if (call->event.type && call->class->reg)
> - trace_create_file("id", 0444, file->dir, call,
> - id);
> + trace_create_file("id", 0444, file->dir,
> + (void *)(long)call->event.type, id);
> #endif
>
> /*




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