Messages in this thread | | | Date | Mon, 10 Mar 2008 08:52:00 -0700 | From | Greg KH <> | Subject | Re: [PATCH] Mark kobjects as unitialized |
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On Sun, Mar 09, 2008 at 12:51:15PM +0530, Balaji Rao wrote: > On Sunday 09 March 2008 12:33:07 pm Greg KH wrote: > <snip> > > > > > 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. > > > > > > > > > > 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. > > > > > > > > I like the memset idea, how about this patch instead? > > > > > > > > thanks, > > > > > > > > greg k-h > > > > > > > > --- a/drivers/base/sys.c > > > > +++ b/drivers/base/sys.c > > > > @@ -133,6 +133,7 @@ int sysdev_class_register(struct sysdev_ > > > > pr_debug("Registering sysdev class '%s'\n", > > > > kobject_name(&cls->kset.kobj)); > > > > INIT_LIST_HEAD(&cls->drivers); > > > > + memset(&cls->kset.kobj, 0x00, sizeof(struct kobject)); > > > > cls->kset.kobj.parent = &system_kset->kobj; > > > > cls->kset.kobj.ktype = &ktype_sysdev_class; > > > > cls->kset.kobj.kset = system_kset; > > > > > > > > > > This should work.But I am afraid if we zeroed it, the kfree poison > > > test wouldn't catch even the genuine cases. Isn't it ? CMIIW. > > > > What "genuine cases"? kobjects should always be initialized to zero > > before they are registered. > > > The cases in which a freed kobject is passed to the register function ? Probably they will be caught when do a memset.. > > > A better fix according to me would be to zero the kobject in the > > > places where we know it is being re-registered (kvm, oprofile) etc. > > > This should do for now. But we should fix the sys_device users later, > > > for the next cycle. > > > > Are you sure you know all of the sysdev_class objects that can be > > re-registered? > > > Hmm.. Right. No, I only know that KVM and Oprofile use it. > > Can you test this patch out? > > > Yes the idea works. One more memset is needed in sysdev_register. Here's the final patch. > > diff --git a/drivers/base/sys.c b/drivers/base/sys.c > index 2f79c55..7c839d9 100644 > --- a/drivers/base/sys.c > +++ b/drivers/base/sys.c > @@ -133,6 +133,7 @@ int sysdev_class_register(struct sysdev_class * cls) > pr_debug("Registering sysdev class '%s'\n", > kobject_name(&cls->kset.kobj)); > INIT_LIST_HEAD(&cls->drivers); > + memset(&cls->kset.kobj, 0x00, sizeof(struct kobject)); > cls->kset.kobj.parent = &system_kset->kobj; > cls->kset.kobj.ktype = &ktype_sysdev_class; > cls->kset.kobj.kset = system_kset; > @@ -227,6 +228,7 @@ int sysdev_register(struct sys_device * sysdev) > > pr_debug("Registering sys device '%s'\n", kobject_name(&sysdev->kobj)); > > + memset(&sysdev->kobj, 0x00, sizeof(struct kobject)); > /* Make sure the kset is set */ > sysdev->kobj.kset = &cls->kset;
Yes, you're right.
This also means I can drop the kobject_cleanup() patch from you as well, as that should no longer be needed, right?
thanks,
greg k-h
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