Messages in this thread | | | Subject | Re: [PATCH 1/3] ftrace: add function tracing to single thread | From | Dave Hansen <> | Date | Tue, 25 Nov 2008 16:53:59 -0800 |
| |
On Tue, 2008-11-25 at 19:11 -0500, Steven Rostedt wrote: > > > > Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > > > > > This patch adds the ability to function trace a single thread. > > > > > The file: > > > > > > > > > > /debugfs/tracing/set_ftrace_pid > > > > > > > > > > contains the pid to trace. > > > > > > > > What happens if the same pid exists in two or more pid namespaces? > > > > > > I think we had this discussion before. > > > > Oh. What did we end up concluding? > > > > > It tests current->pid, would that > > > be different among the name spaces? > > > > I think those are non-unique. containers@lists.osdl.org would have > > better ideas.. > > Added list in CC. > > I think the end result was, if this file can only be changed by root, then > we do not need to worry about namespaces. This file is a privileged file > that can only be modified by root. > > If someday we decide to let non admin users touch this file, then we would > need to care about this. This file may actually be modified in the future > by users, so this may become an issue.
This really has very little to do with root vs non-root users. In fact, we're working towards having cases where we have many "root" users, even those inside namespaces. It is also quite possible for a normal root user to fork into a new pid namespace. In that case, root simply won't be able to use this feature because something like:
echo $$ /debugfs/tracing/set_ftrace_pid
just won't work. Let's look at a bit of the code.
+static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip) +{ + if (current->pid != ftrace_pid_trace) + return; + + ftrace_pid_function(ip, parent_ip); +}
One thing this doesn't deal with is pid wraparound. Does that matter?
If you want to fix this a bit, instead of saving off the pid_t in ftrace_pid_trace, you should save a 'struct pid'. You can get the 'struct pid' for a particular task by doing a find_get_pid(pid_t). You can then compare that pid_t to current by doing a pid_task(struct_pid_that_i_saved, PIDTYPE_PID). That will also protect against pid wraparound.
The find_get_pid() is handy because it will do the pid_t lookup in the context of the current task's pid namespace, which is what you want, I think.
-- Dave
| |