linux-kernel - Re: [PATCH 1/2] mtd: use refcount to prevent corruption

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Message-ID: <20230716153926.5e975231@xps-13>
Date:   Sun, 16 Jul 2023 15:39:26 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     "Usyskin, Alexander" <alexander.usyskin@...el.com>
Cc:     Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Winkler, Tomas" <tomas.winkler@...el.com>,
        "Lubart, Vitaly" <vitaly.lubart@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Biju Das <biju.das.jz@...renesas.com>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Chris Paterson <Chris.Paterson2@...esas.com>
Subject: Re: [PATCH 1/2] mtd: use refcount to prevent corruption

Hi Alexander,

alexander.usyskin@...el.com wrote on Sun, 16 Jul 2023 06:29:02 +0000:

> > > With this patch applied, when I load up the module, I get the same 3
> > > devices:
> > > /dev/mtd0
> > > /dev/mtd0ro
> > > /dev/mtdblock0
> > >
> > > Upon removal, the below 2 devices still hang around:
> > > /dev/mtd0
> > > /dev/mtd0ro  
> >   
> Our use-case do not produce mtdblock, maybe there are some imbalances of get/put?
> I have somewhere version with pr_debug after every kref_get/put. That may help to catch where
> it missed, I hope.

I believe mtdblock is the good citizen here. Just disable
CONFIG_MTD_BLOCK from your configuration and you will likely observe
the same issue, just a bit narrowed, perhaps. Indeed, if you manage to
follow all the get/put calls it can help to find an imbalance.

Thanks,
Miquèl