linux-kernel - Re: [PATCH] mtd: rawnand: mxc: remove __init qualifier from mxcnd_probe

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Date:   Tue, 26 Jun 2018 09:10:05 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Martin Kaiser <martin@...ser.cx>
Cc:     Boris Brezillon <boris.brezillon@...tlin.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: rawnand: mxc: remove __init qualifier from
 mxcnd_probe_dt

Hi Martin, Boris,

On Fri, 22 Jun 2018 16:50:25 +0200, Martin Kaiser <martin@...ser.cx>
wrote:

> mxcnd_probe_dt is called from mxcnd_probe, which is not marked as __init.
> 

I think this line is just a side note and should be at the end of the
commit log.

> Using the sysfs unbind, bind nodes, mxcnd_probe and mxcnd_probe_dt can
> potentially be called at any time. After the __init functions are cleaned,
> mxcnd_probe_dt is no longer available. Calling it anyway causes a crash.

The above paragraph explains the problem and the solution, you can just
add something like "mcvnd_probe is untouched because it is already not
marked as __init" instead of the first line.

> 
> Signed-off-by: Martin Kaiser <martin@...ser.cx>

Boris, do you think this patch is a good candidate for stable?

If yes, Martin, could you please add a couple of stable/fixes tags above
your SoB?

Thanks,
Miquèl

> ---
> I hope that my understanding is correct.
> 
> In practice, I could not get the kernel to crash, my compiler would
> inline mxcnd_probe_dt into mxcnd_probe and ignore the __init.
> 
> If I marked mxcnd_probe_dt as noinline, I could trigger a crash as
> follows
> 
> [root@...t ]# echo bb000000.nand > /sys/bus/platform/drivers/mxc_nand/unbind
> [root@...t ]# echo bb000000.nand > /sys/bus/platform/drivers/mxc_nand/bind
> Internal error: Oops - undefined instruction: 0 [#1] ARM
> ...
> 
>  drivers/mtd/nand/raw/mxc_nand.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/mxc_nand.c b/drivers/mtd/nand/raw/mxc_nand.c
> index 26cef21..90cfb5e 100644
> --- a/drivers/mtd/nand/raw/mxc_nand.c
> +++ b/drivers/mtd/nand/raw/mxc_nand.c
> @@ -1686,7 +1686,7 @@ static const struct of_device_id mxcnd_dt_ids[] = {
>  };
>  MODULE_DEVICE_TABLE(of, mxcnd_dt_ids);
>  
> -static int __init mxcnd_probe_dt(struct mxc_nand_host *host)
> +static int mxcnd_probe_dt(struct mxc_nand_host *host)
>  {
>  	struct device_node *np = host->dev->of_node;
>  	const struct of_device_id *of_id =
> @@ -1700,7 +1700,7 @@ static int __init mxcnd_probe_dt(struct mxc_nand_host *host)
>  	return 0;
>  }
>  #else
> -static int __init mxcnd_probe_dt(struct mxc_nand_host *host)
> +static int mxcnd_probe_dt(struct mxc_nand_host *host)
>  {
>  	return 1;
>  }