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

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Date:   Sun, 10 Sep 2017 20:00:10 +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 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.