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Date:   Thu, 27 Jul 2023 08:19:14 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     "Usyskin, Alexander" <alexander.usyskin@intel.com>
Cc:     Fabrizio Castro <fabrizio.castro.jz@renesas.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Winkler, Tomas" <tomas.winkler@intel.com>,
        "Lubart, Vitaly" <vitaly.lubart@intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Biju Das <biju.das.jz@bp.renesas.com>,
        "linux-renesas-soc@vger.kernel.org" 
        <linux-renesas-soc@vger.kernel.org>,
        Chris Paterson <Chris.Paterson2@renesas.com>
Subject: Re: [PATCH 1/2] mtd: use refcount to prevent corruption
Message-ID: <20230727081914.03e44b96@xps-13>
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References: <20230620131905.648089-1-alexander.usyskin@intel.com>
        <20230620131905.648089-2-alexander.usyskin@intel.com>
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Hi Alexander,

alexander.usyskin@intel.com wrote on Tue, 25 Jul 2023 12:50:04 +0000:

> Hi
> >=20
> > Hi Miquel, =20
> > >
> > > Hi Alexander,
> > >
> > > alexander.usyskin@intel.com wrote on Mon, 24 Jul 2023 11:43:59 +0000:
> > > =20
> > > > > > > > With this patch applied, when I load up the module, I get t=
he same 3
> > > > > > > > devices:
> > > > > > > > /dev/mtd0
> > > > > > > > /dev/mtd0ro
> > > > > > > > /dev/mtdblock0
> > > > > > > >
> > > > > > > > Upon removal, the below 2 devices still hang around:
> > > > > > > > /dev/mtd0
> > > > > > > > /dev/mtd0ro =20
> > > > > > > =20
> > > > > > Our use-case do not produce mtdblock, maybe there are some =20
> > > imbalances =20
> > > > > of get/put? =20
> > > > > > I have somewhere version with pr_debug after every kref_get/put=
. That =20
> > > may =20
> > > > > help to catch where =20
> > > > > > it missed, I hope. =20
> > > > >
> > > > > I believe mtdblock is the good citizen here. Just disable
> > > > > CONFIG_MTD_BLOCK from your configuration and you will likely obse=
rve
> > > > > the same issue, just a bit narrowed, perhaps. Indeed, if you mana=
ge to
> > > > > follow all the get/put calls it can help to find an imbalance.
> > > > >
> > > > > Thanks,
> > > > > Miqu=C3=A8l =20
> > > >
> > > > Miquel, do you have CONFIG_MTD_PARTITIONED_MASTER set in your =20
> > > config?
> > >
> > > Not sure I get your question. You can enable or disable it, it should
> > > work in both cases (yet, the handling is of course a bit different as
> > > the top level device will be retained/not retained).
> > >
> > > Thanks,
> > > Miqu=C3=A8l =20
> >=20
> > I'm trying to understand why I can't reproduce the problem in my scenar=
io.
> > I found an important difference in upstreamed patch and internal versio=
n:
> > The IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER) check around
> > kref_get/put does not exists in the internal tree.
> > The code before my patch do not have such check, so I tend to assume th=
at
> > this check should be removed.
> > If you reproduce happens with CONFIG_MTD_PARTITIONED_MASTER
> > disabled that may explain problems that you see.
> >=20
> > --
> > Thanks,
> > Sasha
> >  =20
>=20
> I've tried to reproduce this with latest Linux 6.5-rc1 and my two patches.
> The manual modprobe mtdblock creates mtdblock0 over my partitions too.
> I can't reproduce problem neither with MTD_PARTITIONED_MASTER nor without.
>=20
> Let's try to debug on your system, can you enable dynamic debug for mtd s=
ubsystem,
> reproduce and publish dmesg?
>=20
> The prints for kref get/put can be added as below:
>=20
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 2466ea466466..374835831428 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -1242,10 +1242,13 @@ int __get_mtd_device(struct mtd_info *mtd)
>         }
>=20
>         kref_get(&mtd->refcnt);
> +       pr_debug("get mtd %s %d\n", mtd->name, kref_read(&mtd->refcnt));
>=20
>         while (mtd->parent) {
> -               if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER) || mtd->par=
ent !=3D master)
> +               if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER) || mtd->par=
ent !=3D master) {
>                         kref_get(&mtd->parent->refcnt);
> +                       pr_debug("get mtd %s %d\n", mtd->parent->name, kr=
ef_read(&mtd->parent->refcnt));
> +               }
>                 mtd =3D mtd->parent;
>         }
>=20
> @@ -1335,12 +1338,15 @@ void __put_mtd_device(struct mtd_info *mtd)
>         while (mtd !=3D master) {
>                 struct mtd_info *parent =3D mtd->parent;
>=20
> +               pr_debug("put mtd %s %d\n", mtd->name, kref_read(&mtd->re=
fcnt));
>                 kref_put(&mtd->refcnt, mtd_device_release);
>                 mtd =3D parent;
>         }
>=20
> -       if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
> +       if (IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER)) {
> +               pr_debug("put mtd %s %d\n", master->name, kref_read(&mast=
er->refcnt));
>                 kref_put(&master->refcnt, mtd_device_release);
> +       }
>=20
>         module_put(master->owner);
>=20
>=20

Could this be helpful?

https://lore.kernel.org/all/20230725215539.3135304-1-zhangxiaoxu5@huawei.co=
m/

If you successfully test it, please send your Tested-by.

Thanks,
Miqu=C3=A8l