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

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Date:   Sun, 10 Sep 2017 21:13:45 +0200
From:   Jakub Kicinski <kubakici@...pl>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [bisected] Re: Module removal-related regression?

On Sun, 10 Sep 2017 21:09:08 +0200, Greg Kroah-Hartman wrote:
> On Sun, Sep 10, 2017 at 11:12:17AM -0700, Dmitry Torokhov wrote:
> > On September 10, 2017 11:00:10 AM PDT, Jakub Kicinski <kubakici@...pl> wrote:  
> > >On Sun, 10 Sep 2017 09:21:11 -0700, Dmitry Torokhov wrote:  
> > >> On Sun, Sep 10, 2017 at 12:03:38AM +0200, Jakub Kicinski wrote:  
> > >> > 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/
> > >> > $    
> > >> 
> > >> Not sure why you bring the deferrals here, they have nothing to do  
> > >with  
> > >> module removal. Also, deferrals are rarely issued by the leaf driver,  
> > >and  
> > >> more often by providers of resources (GPIO, regulator, interrupt,  
> > >etc).
> > >
> > >Yes, it's unusual, but this driver used to do it.  Which is exactly why
> > >I brought it up.  Turns out it was irrelevant :)
> > >  
> > >> > I tested without any udev rules in /etc/udev/, just the standard  
> > >distro  
> > >> > ones.  Same thing.    
> > >> 
> > >> Right, so this is the default udev rule:
> > >> 
> > >> /lib/udev/rules.d/80-drivers.rules:
> > >> 
> > >> # do not edit this file, it will be overwritten on update
> > >> 
> > >> ACTION=="remove", GOTO="drivers_end"
> > >> 
> > >> ENV{MODALIAS}=="?*", RUN{builtin}="kmod load $env{MODALIAS}"  
> 
> So if the new uevents do not have the MODALIAS line in them, then they
> will not trigger this?  Dmitry, can you see if that would fix this
> problem without having to fix everyone's old versions of udev/systemd?

Perhaps another option is dropping the unbind event?  From the commit
message it seems like only bind is really needed ATM.  Do events have
to be symmetrical?