linux-kernel - Re: [bisected] Re: Module removal-related regression?

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Date:   Sun, 10 Sep 2017 00:03:38 +0200
From:   Jakub Kicinski <kubakici@...pl>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [bisected] Re: Module removal-related regression?

On Sat, 09 Sep 2017 13:59:25 -0700, Dmitry Torokhov wrote:
> On September 9, 2017 1:17:26 PM PDT, Jakub Kicinski <kubakici@...pl> wrote:
> >On Sat, 9 Sep 2017 12:55:51 -0700, Dmitry Torokhov wrote:  
> >> On Sat, Sep 9, 2017 at 12:27 PM, Jakub Kicinski <kubakici@...pl>  
> >wrote:  
> >> > On Sat, 9 Sep 2017 19:41:21 +0200, Jakub Kicinski wrote:    
> >> >> Hi!
> >> >>
> >> >> I'm having trouble with modules on linux/master.  rmmod succeeds  
> >but the  
> >> >> module is still loaded and the refcount goes to 1:
> >> >>
> >> >> #rmmod nfp; insmod ./src/nfp.ko nfp_pf_netdev=0 ; \
> >> >>       /opt/netronome/bin/nfp-hwinfo -n 2  assembly.partno \
> >> >>       lsmod | grep nfp; \
> >> >>       rmmod nfp; \
> >> >>       lsmod | grep nfp
> >> >> nfp                   249856  0
> >> >> nfp                   200704  1
> >> >>
> >> >> If I rmmod again the module will be actually unloaded.  The user  
> >space  
> >> >> is mostly Ubuntu 14.04.  Has anyone seen this?  I'm trying to  
> >bisect  
> >> >> now...    
> >> >
> >> > Got 'em!
> >> >
> >> > commit 1455cf8dbfd06aa7651dcfccbadb7a093944ca65 (HEAD,  
> >refs/bisect/bad)  
> >> > Author: Dmitry Torokhov <dmitry.torokhov@...il.com>
> >> > Date:   Wed Jul 19 17:24:30 2017 -0700
> >> >
> >> >     driver core: emit uevents when device is bound to a driver    
> >> 
> >> Does it happen with all modules or only nfp one?
> >> 
> >> It seems to work here:
> >> 
> >> dtor@...r-glaptop3:~ $ lsmod | grep psmouse
> >> psmouse               135168  0
> >> dtor@...r-glaptop3:~ $ sudo rmmod psmouse
> >> dtor@...r-glaptop3:~ $ lsmod | grep psmouse
> >> dtor@...r-glaptop3:~ $ sudo modprobe psmouse  
> >
> >It looks like the driver is actually reloaded.  The driver used to
> >return EPROBE_DEFER, but I think it doesn't any more (rebuilding the
> >kernel to test that right now).
> >
> >Could the uevent on unbind tickle Ubuntu 14.04's udev or somehow
> >else cause the driver to be loaded again?   
> 
> It depends on how silly the udev rules are, but yes, this can definitely happen.

I confirmed the driver doesn't use EPROBE_DEFER any more:

$ grep -nrI EPROBE_DEFER drivers/net/ethernet/netronome/
$

I tested without any udev rules in /etc/udev/, just the standard distro
ones.  Same thing.

Please find attached the logs from rmmod with kobject debug enabled.

View attachment "log" of type "text/x-log" (88078 bytes)