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

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Date:   Sun, 10 Sep 2017 09:21:11 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Jakub Kicinski <kubakici@...pl>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [bisected] Re: Module removal-related regression?

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).

> 
> 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"

Thanks.

-- 
Dmitry