linux-kernel - Re: [PATCH] net/9p/trans_virtio.c: decrease the refcount of 9p virtio device when removing it

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Date:   Wed, 8 Aug 2018 11:40:14 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     piaojun <piaojun@...wei.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        Greg Kurz <groug@...d.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        v9fs-developer@...ts.sourceforge.net
Subject: Re: [PATCH] net/9p/trans_virtio.c: decrease the refcount of 9p
 virtio device when removing it

piaojun wrote on Wed, Aug 08, 2018:
> I try to remove 9pnet_virtio.ko by 'rmmod 9pnet_virtio' as I want to
> replace it without rebooting system.

I do that all the time when testing, it works for me.
What exact kernel commit are you running?

> Here I have not mount 9pfs yet, so the refcount is still 0.
> 
> Before rmmod:
> # lsmod | grep 9p
> 9pnet_virtio           20480  0
> 9pnet                 106496  1 9pnet_virtio
> virtio_ring            28672  5 virtio_scsi,9pnet_virtio,virtio_pci,virtio_blk,virtio_net
> virtio                 16384  5 virtio_scsi,9pnet_virtio,virtio_pci,virtio_blk,virtio_net
> 
> After rmmod:
> # lsmod | grep 9p
> 9pnet_virtio           20480  0
> 9pnet                 106496  1 9pnet_virtio
> virtio_ring            28672  5 virtio_scsi,9pnet_virtio,virtio_pci,virtio_blk,virtio_net
> virtio                 16384  5 virtio_scsi,9pnet_virtio,virtio_pci,virtio_blk,virtio_net
> 
> Normally 9pnet_virtio should be invisible after rmmod like this:
> # lsmod | grep 9p
> 9pnet                 106496  0

Right, that obviously didn't work...

But on the other hand, if I apply your commit and load/unload
9pnet_virtio 5-10 times (I ran it in a loop) I get KASAN errors because
we put too many of these refs ; that doesn't happen without your patch
so it's apparently wrong.
I'm curious how that could make modprobe work better for you as well, it
shouldn't depend on that...

Maybe `modprobe -r` might give a better error, or something in dmesg?

-- 
Dominique