Messages in this thread | | | Date | Tue, 25 Nov 2008 20:01:34 -0500 (EST) | From | Steven Rostedt <> | Subject | Re: [PATCH 1/3] ftrace: add function tracing to single thread |
| |
On Tue, 25 Nov 2008, Dave Hansen wrote: > > > > 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?
Should not. This is just a way to trace a particular process. Currently it traces all processes. If we wrap, then we trace the process with the new pid. This should not be an issue.
> > 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.
Nope, we can not call that in this context. ftrace_pid_func is called directly from mcount, without any protection.
struct pid *find_get_pid(pid_t nr) { struct pid *pid;
rcu_read_lock(); pid = get_pid(find_vpid(nr)); rcu_read_unlock();
return pid; } EXPORT_SYMBOL_GPL(find_get_pid);
This means find_get_pid will call mcount which will call ftrace_pid_func, and back again. This can also happen with rcu_read_{un}lock() and get_pid() and find_vpid().
We can not do anything special here.
-- Steve
| |