Re: [PATCH] Prevent trace call into unloaded module text

[Wu Fengguang <fengguang.wu@intel.com>]

On Wed, Nov 26, 2008 at 07:46:19PM +0800, Wu Fengguang wrote:
> On Wed, Nov 26, 2008 at 01:17:55PM +0200, Avi Kivity wrote:
> > Wu Fengguang wrote:
> > > Add marker_synchronize_unregister() before module unloading.
> > > This prevents possible trace calls into unloaded module text.
> > >
> > > Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
> > > ---
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index a87f45e..64f38b3 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -2102,5 +2102,6 @@ void kvm_exit(void)
> > >  	kvm_arch_exit();
> > >  	kvm_exit_debug();
> > >  	__free_page(bad_page);
> > > +	marker_synchronize_unregister();
> > >  }
> > >  EXPORT_SYMBOL_GPL(kvm_exit);
> > >   
> > 
> > What about kvm-intel.ko and kvm-amd.ko?  They also contain markers.
> 
> vmx_exit and svm_exit() all calls into kvm_exit(), so they have been
> handled in a common way.
> 
> > (and, why doesn't module unload do this automatically?)
> 
> Maybe most modules don't need it for now?

OK I got a better answer: because marker_synchronize_unregister() must
be called after marker_probe_unregister() calls and the tear down of
any private data the trace functions rely on. So there are no
automatic way.

Below is the updated patch.

Thanks,
Fengguang
---
Prevent trace call into torn down text or data

Add marker_synchronize_unregister() immediately after probe unregisters.
This prevents possible trace calls into unloaded module text, or the
trace functions accessing invalidated data.

Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
---
diff --git a/virt/kvm/kvm_trace.c b/virt/kvm/kvm_trace.c
index 41dcc84..f598744 100644
--- a/virt/kvm/kvm_trace.c
+++ b/virt/kvm/kvm_trace.c
@@ -252,6 +252,7 @@ void kvm_trace_cleanup(void)
 			struct kvm_trace_probe *p = &kvm_trace_probes[i];
 			marker_probe_unregister(p->name, p->probe_func, p);
 		}
+		marker_synchronize_unregister();
 
 		relay_close(kt->rchan);
 		debugfs_remove(kt->lost_file);