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SubjectRe: [PATCH] Mark kobjects as unitialized
Date
On Sunday 09 March 2008 10:36:49 am Greg KH wrote:
> On Sun, Mar 09, 2008 at 03:37:16AM +0530, Balaji Rao wrote:
> > On Thursday 06 March 2008 11:35:59 pm Greg KH wrote:
> > > On Thu, Mar 06, 2008 at 11:20:50PM +0530, Balaji Rao wrote:
> > > > On Thursday 06 March 2008 10:35:14 pm Greg KH wrote:
> > > > <snip>
> > > > > Where exactly in the code does that happen? kobjects should not be
> > > > > "reused" as that implies that they are static, and not dynamically
> > > > > allocated, right?
> > > > >
> > > > > Which kobject is this?
> > > > Yes, its static. Here's the code from virt/kvm_main.c:1269
> > > >
> > > > static struct sys_device kvm_sysdev = {
> > > > .id = 0,
> > > > .cls = &kvm_sysdev_class,
> > > > };
> > > >
> > > > this sys_device is being registered/unregistered when kvm-intel is
> > > > loaded/unloaded.
> > >
> > > Ah, ok. I'll add this patch then.
> > >
> > > > > Ugh, is this the sys_device stuff? I hate that code...
> > > > >
> > > > Yes it is! But, why do you hate it ?
> > >
> > > For reasons like this :)
> > >
> > > kobjects should not be static. the sysdevice stuff was a hack when it
> > > was originally created and never touched since the mid 2.5 days. It
> > > needs to be fixed up a lot, and is on my TODO list, slowly getting
> > > closer to the top...
> > Hi,
> >
> > This patch does not fix it all! The problem is in fact more involved.
> > I also get these BUG reports when I reload kvm-intel.
> >
> > BUG kmalloc-8: Object already free
> > [ 74.696570] -----------------------------------------------------------------------------
> > [ 74.696596]
> > [ 74.697310] INFO: Allocated in strndup_user+0x30/0x62 age=587 cpu=2 pid=1439
> > [ 74.697845] INFO: Freed in kobject_set_name_vargs+0x29/0x32 age=559 cpu=3 pid=1439
> > [ 74.698008] INFO: Slab 0xc16f93a0 used=10 fp=0xf7c9d2d8 flags=0x10000c3
> > [ 74.698008] INFO: Object 0xf7c9d1f8 @offset=504 fp=0xf7c9d578
> >
> > This happens because, sysdev_class_register assigns a name to the
> > kobject, and kfrees the old name if any. The poisoned 'name' object
> > persists in case of statically allocated kobjects and as its passed to
> > kfree again when re registered, we get the above warning.
>
> Ugh, that's horrible. And people wonder why I hate the sysdev code :)
>
> Does it also mean that when we do cleanup sysdev devices, we are freeing
> a name that might not have been dynamically allocated? If so, we need
> to fix that as well.
>
No, that doesn't happen. We free the name only if it is allocated..
> A simple 'strdup' of the class name in sysdev_class_register() should
> fix all of this, right?
>
> > So, AFAICS the best way to solve this is by fixing the kobject users
> > (kvm, oprofile etc.) to use dynamic kobjects instead of static ones or
> > memset the kobject to zero before passing it to sysdev_register.
>
> Yes, that would be great to fix up, but probably unlikly so late in the
> release cycle.
>
> How about the patch below, does it work for you? (build tested only)
>
> thanks,
>
> greg k-h
>
>
> ---
> drivers/base/sys.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> --- a/drivers/base/sys.c
> +++ b/drivers/base/sys.c
> @@ -130,13 +130,16 @@ static struct kset *system_kset;
>
> int sysdev_class_register(struct sysdev_class * cls)
> {
> + char *name;
> +
> pr_debug("Registering sysdev class '%s'\n",
> kobject_name(&cls->kset.kobj));
> INIT_LIST_HEAD(&cls->drivers);
> cls->kset.kobj.parent = &system_kset->kobj;
> cls->kset.kobj.ktype = &ktype_sysdev_class;
> cls->kset.kobj.kset = system_kset;
> - kobject_set_name(&cls->kset.kobj, cls->name);
> + name = kstrdup(cls->name, GFP_KERNEL);
> + kobject_set_name(&cls->kset.kobj, name);
> return kset_register(&cls->kset);
> }
>
>



--
regards,
balaji rao
3rd year,
Dept. of Mechanical Engineering,
National Institute of Technology, Karnataka


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