On Fri, Jul 18, 2014 at 11:59 AM, Chetan Nanda <chetannanda@xxxxxxxxx> wrote:
On Fri, Jul 18, 2014 at 9:47 AM, Greg KH <greg@xxxxxxxxx> wrote:
Are you properly setting the .owner field of your file operationsOn Fri, Jul 18, 2014 at 09:43:48AM +0530, Chetan Nanda wrote:
>
>
>
> On Wed, Jul 16, 2014 at 9:51 PM, Greg KH <greg@xxxxxxxxx> wrote:
>
> On Wed, Jul 16, 2014 at 08:57:38PM +0530, Chetan Nanda wrote:
> >
> >
> >
> > On Wed, Jul 16, 2014 at 8:49 PM, Chetan Nanda <chetannanda@xxxxxxxxx>
> wrote:
> >
> >
> >
> > On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <john@xxxxxxxxx>
> wrote:
> >
> > On Wed, Jul 16, 2014 at 04:00:18PM +0530, Chetan Nanda wrote:
> > > A depends on B, so B is automatically loaded when A is loaded.
> > > B module is also directly being used by the user side code via
> misc
> > > interface.
> > >.
> > > Now when I am unloading module A, via "modprobe -r A" it is
> also
> > unloading
> > > the module B which is being used by the application and
> resulting in
> > the
> > > kernel crash.
> >
> > You said that A depends on B, right? Why do you have A dependng
> on B?
> > If it A needs to have B then it makes sense that you can not
> remove A
> > while
> > B is in use. If A doesn't need B, why not remove the dependency.
> >
> >
> > A is calling few APIs defined by B.
> >
> > But why when user space application is already using module B. (it has
> already
> > open its device fd) kernel allows to remove it.
> >
> > I tried with doing try_module_get() in the module's open function, it
> prevent
> > module B unloading but cause thread doing modprobe -r to hang
> > Is there any other way to mark module as busy when being used by user
> > application?
>
> Never use try_module_get(), that is racy.
>
> What is the user/kernel interface you are using, and why doesn't it
> automatically increase the module count when userspace opens the
> interface? It should all be done in a way that your module doesn't need
> to do anything special.
>
>
> Hi Greg,
>
> Thanks for your mail.
>
> Module is using misc driver interface to export its functionality to
> userspace,
>
> Need to debug further why module count is not getting incremented automatically
> when module is open by userspace application via open system call.
structure to be THIS_MODULE? If not, try fixing that up. If you are,
try posting your code for review.
greg k-h
Hi Greg,Thanks for the hint, indeed that was the issue, .owner field was not set in file operation structure.After setting that, 'modprobe -r A' is hanging. As the module B in use and can't be removed.I am using busybox on embedded Linux, I think this could be a modprobe utility issue.Ideally modprobe should not try to remove the module in used.
I try to debug the hang when unloading of driver. I am using kernel v3.10 and it hangs in 'wait_for_zero_refcount'.
I checked that this function has been removed in kernel 3.13.
But I am not able to find the patch for this change.
Is there an easy way to find the patch which cause removal of wait from module unloading in v3.13.
Thanks,Chetan Nanda
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