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Date:   Sun, 10 Sep 2017 20:39:37 +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 Sun, 10 Sep 2017 11:12:17 -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 $env{MODALIAS}"
> >> SUBSYSTEM=="tifm", ENV{TIFM_CARD_TYPE}=="SD", RUN{builtin}="kmod load  
> >tifm_sd"  
> >> SUBSYSTEM=="tifm", ENV{TIFM_CARD_TYPE}=="MS", RUN{builtin}="kmod load  
> >tifm_ms"  
> >> SUBSYSTEM=="memstick", RUN{builtin}="kmod load ms_block mspro_block"
> >> SUBSYSTEM=="i2o", RUN{builtin}="kmod load i2o_block"
> >> SUBSYSTEM=="module", KERNEL=="parport_pc", RUN{builtin}="kmod load  
> >ppdev"  
> >> SUBSYSTEM=="serio", ENV{MODALIAS}=="?*", RUN{builtin}="kmod load  
> >$env{MODALIAS}"  
> >> SUBSYSTEM=="graphics", RUN{builtin}="kmod load fbcon"
> >> KERNEL=="mtd*ro", ENV{MTD_FTL}=="smartmedia", RUN{builtin}="kmod load  
> >sm_ftl"  
> >> 
> >> LABEL="drivers_end"
> >> 
> >> So udev (and systemd) want to load kernel module on any action  
> >besides  
> >> device removal. Shortsighted decision I'd say. I'll send a patch to
> >> systemd, in the mean time you can simply adjust your local rule to  
> >read  
> >> 
> >> ACTION!="add", GOTO="drivers_end"  
> >
> >Mm.  That is a silly thing.  You will break a lot of setups, though.  
> 
> I think the priority it to have module loading working properly, and
> for most users once module is loaded it stays loaded. Unloading is
> mostly for developers.
>
> Luckily newer systemd versions drop events they do not recognize, so
> exposure is even smaller.

Could you point me to where that's done?

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