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

Heiko Carstens
2009-08-26T14:10:54Z

On Wed, Aug 26, 2009 at 03:30:22PM +0200, Frederic Weisbecker wrote:
> On Wed, Aug 26, 2009 at 02:59:43PM +0200, Heiko Carstens wrote:
> > > Yeah, and as told before, syscalls tracing from kernel thread is
> > > an interesting point but we can't do it that way.
> > >
> > > I'm queuing this patch for .32, but I need you Signed-off-by to apply it :)
> >
> > 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.

Oh yes, you are right. kernel threads created with kernel_thread()
have t->mm != NULL if the forking process has an mm too.

There are very few callsites left which still use kernel_thread().
(the last one in s390 driver code will be gone after the next
merge window).

As far as I can there are only four callsites left
(excluding staging): jffs2 and three in net/bluetooth/*