Re: [PATCH 08/12] add trace events for each syscall entry/exit

Steven Rostedt
2009-08-26T13:48:51Z

On Wed, 26 Aug 2009, Frederic Weisbecker wrote:
> >
> > That won't always work as pointed out in the other example:
> > - Process doing sys_init_module then scheduled away
> > - User enables syscall tracing -> TIF_SYSCALL_FTRACE gets set
> > - init function of the module gets called and is doing kernel_thread()
> > (old API) -> kernel thread inherits TIF_SYSCALL_FTRACE.
> >
> > I don't think that's what you want. You might want to clear the flag for
> > new processes during fork (only for kernel threads I would guess).
> >
> > At least the current patch leaves a hole.
>
>
> Ah, there are callsites that use kernel_thread() directly?
> Does it means that t->mm could be non NULL for such resulting
> kernel threads, in that case it would be hard to hook on
> do_fork() to check that.

All kernel threads have a NULL t->mm. Since do_fork is called by kthreadd
and not by kthread_create, the caller of do_fork will also have a
t->mm = NULL.

-- Steve