Re: [PATCH v2] perf: Synchronously cleanup child events

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Jan 26, 2016 at 05:16:37PM +0100, Peter Zijlstra wrote:
> > +struct file *perf_event_get(unsigned int fd)
> >  {
> > +	struct file *file;
> >  
> > +	file = fget_raw(fd);
> 
> fget_raw() to guarantee the return value isn't NULL? afaict the O_PATH
> stuff does not apply to perf events, so you'd put any fd for which the
> distinction matters anyway.
> 
> > +	if (file->f_op != &perf_fops) {
> > +		fput(file);
> > +		return ERR_PTR(-EBADF);
> > +	}
> >  
> > +	return file;
> >  }

It is not possible for one thread to concurrently call close() while
this thread tries to fget() ? In which case, we must check the return
value anyway?