On Fri, Jul 18, 2014 at 9:47 AM, Greg KH <g...@kroah.com> wrote: > On Fri, Jul 18, 2014 at 09:43:48AM +0530, Chetan Nanda wrote: > > > > > > > > On Wed, Jul 16, 2014 at 9:51 PM, Greg KH <g...@kroah.com> 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 < > chetanna...@gmail.com> > > wrote: > > > > > > > > > > > > On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza < > j...@jjdev.com> > > 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. > > Are you properly setting the .owner field of your file operations > 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. Thanks, Chetan Nanda
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