How to prevent a module from unloading when in used

How to prevent a module from unloading when in used

[Chetan Nanda]

Hi,

I am  facing an issues with module unloading,
I have two modules say A, B

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.

Also, lsmod ouput shows driver B is not used by anybody. Seems "Used By" of
lsmod output is not getting updated.

How to prevent unloading of module B in used. When unloading module 'A' via
modprobe -r

Thanks,
Chetan Nanda
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How to prevent a module from unloading when in used

[John de la Garza]

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.

How to prevent a module from unloading when in used

[Chetan Nanda]

On Wed, Jul 16, 2014 at 8:49 PM, Chetan Nanda <chetannanda@gmail.com> wrote:

>
>
> On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <john@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?
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How to prevent a module from unloading when in used

[Greg KH]

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@gmail.com> wrote:
> 
> 
> 
>     On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <john@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.

thanks,

greg k-h

How to prevent a module from unloading when in used

[Chetan Nanda]

On Wed, Jul 16, 2014 at 9:51 PM, Greg KH <greg@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 <chetannanda@gmail.com>
> wrote:
> >
> >
> >
> >     On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <john@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.

Thanks
Chetan Nanda

thanks,
>
> greg k-h
>
>
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How to prevent a module from unloading when in used

[Greg KH]

On Fri, Jul 18, 2014 at 09:43:48AM +0530, Chetan Nanda wrote:
> 
> 
> 
> On Wed, Jul 16, 2014 at 9:51 PM, Greg KH <greg@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 <chetannanda@gmail.com>
>     wrote:
>     >
>     >
>     >
>     > ? ? On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <john@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

How to prevent a module from unloading when in used

[Chetan Nanda]

On Fri, Jul 18, 2014 at 9:47 AM, Greg KH <greg@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 <greg@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 <
> chetannanda at gmail.com>
> >     wrote:
> >     >
> >     >
> >     >
> >     >     On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <
> john at 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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How to prevent a module from unloading when in used

[Chetan Nanda]

On Fri, Jul 18, 2014 at 11:59 AM, Chetan Nanda <chetannanda@gmail.com>
wrote:

>
>
>
> On Fri, Jul 18, 2014 at 9:47 AM, Greg KH <greg@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 <greg@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 <
>> chetannanda at gmail.com>
>> >     wrote:
>> >     >
>> >     >
>> >     >
>> >     >     On Wed, Jul 16, 2014 at 6:39 PM, John de la Garza <
>> john at 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.
>
> 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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How to prevent a module from unloading when in used

[Greg KH]

On Mon, Jul 21, 2014 at 09:09:02AM +0530, Chetan Nanda wrote:
> 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.

You have the full git tree, it should be very easy to find, you don't
need help from me.

good luck,

greg k-h

How to prevent a module from unloading when in used

[Chetan Nanda]

On Mon, Jul 21, 2014 at 9:52 AM, Greg KH <greg@kroah.com> wrote:

> On Mon, Jul 21, 2014 at 09:09:02AM +0530, Chetan Nanda wrote:
> > 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.
>
> You have the full git tree, it should be very easy to find, you don't
> need help from me.
>
> Hi Greg,

Thanks for your mail,

I have found a thread with the discussion and a patch for removing the
wait_for_zero_refcount from module unloading, But not able to find this
patch being merged on v3.13. (have checked all patches between 3.12 and
3.13)
http://www.gossamer-threads.com/lists/linux/kernel/1783584?do=post_view_threaded#1783584

Thanks,
Chetan Nanda


> good luck,
>
> greg k-h
>
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How to prevent a module from unloading when in used

[Greg KH]

On Mon, Jul 21, 2014 at 10:20:48AM +0530, Chetan Nanda wrote:
> On Mon, Jul 21, 2014 at 9:52 AM, Greg KH <greg@kroah.com> wrote:
> 
> > On Mon, Jul 21, 2014 at 09:09:02AM +0530, Chetan Nanda wrote:
> > > 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.
> >
> > You have the full git tree, it should be very easy to find, you don't
> > need help from me.
> >
> > Hi Greg,
> 
> Thanks for your mail,
> 
> I have found a thread with the discussion and a patch for removing the
> wait_for_zero_refcount from module unloading, But not able to find this
> patch being merged on v3.13. (have checked all patches between 3.12 and
> 3.13)
> http://www.gossamer-threads.com/lists/linux/kernel/1783584?do=post_view_threaded#1783584

This email tells you the exact name of the patch to search for, and the
files in which it modifies, making it even easier to search for it.

How are you searching the git log that you are not seeing this patch,
which ended up being in the 3.13-rc1 kernel release?

Finding the git commit id is an exercise left for the reader...

greg k-h

How to prevent a module from unloading when in used

[Abhishek Sharma]

Hi,
Is their some special reason for not using "rmmod" to unload module?
rmmod will remove only the module which it is told to remove.

Regards,
Abhishek Sharma

On Wednesday 16 July 2014 04:00 PM, Chetan Nanda wrote:
> Hi,
>
> I am  facing an issues with module unloading,
> I have two modules say A, B
>
> 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.
>
> Also, lsmod ouput shows driver B is not used by anybody. Seems "Used 
> By" of lsmod output is not getting updated.
>
> How to prevent unloading of module B in used. When unloading module 
> 'A' via modprobe -r
>
> Thanks,
> Chetan Nanda
>
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
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