Re: [PATCH] kprobes: bugfix: try_module_get even if calling_mod is NULL

[Ananth N Mavinakayanahalli <ananth@in.ibm.com>]

On Thu, Nov 06, 2008 at 06:54:56PM -0800, Andrew Morton wrote:
> On Fri, 07 Nov 2008 11:28:02 +0900 Masami Hiramatsu <mhiramat@redhat.com> wrote:
> 
> > Andrew Morton wrote:
> > > I do not understand this description "Get probed module even if the
> > > caller is in the kernel core code".
> > > 
> > > What bug is being fixed here?  What is the kernel behaviour before and
> > > after the patch?
> > 
> > When someone called register_*probe() from kernel-core code(not from
> > module) and that probes a kernel module, users can remove the probed
> > module because kprobe doesn't increment reference counter of the module.
> > (on the other hand, if the kernel-module calls register_*probe,
> > kprobe increments refcount of the probed module.)
> > 
> > Currently, we have no register_*probe() calling from kernel-core(except
> > smoke-test, but the smoke-test doesn't probe module), so there is no
> > real bugs. But the logic is wrong(or not fair) and it can causes a
> > problem when someone might want to probe module from kernel.
> > 
> > After this patch is applied, even if someone put register_*probe() call
> > in the kernel-core code, it increments the reference counter of the
> > probed module, and it prevents user to remove the module until stopping
> > probing it.
> > 
> > > Was the bug present in 2.6.27, 2.6.26 etc?  Or was it a post-2.6.28
> > > regression?
> > 
> > Hmm, it might be an enhancement, because currently the kernel doesn't
> > have real bugs.
> > 
> 
> OK, thanks, so I scheduled this for 2.6.29.
> 
> Also, I decided that
> kprobes-disable-preempt-for-module_text_address-and-kernel_text_address.patch
> is needed in 2.6.28.  Please let me know if that was incorrect.  Please
> also let me know if you think that patch is needed in 2.6.27.x or
> earlier.

That is correct and this doesn't warrant inclusion in 2.6.27.x.

Ananth