Re: [PATCH v2 3/3] mtd: spi-nor: take the flash lock in spi_nor_remove()

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Itai Handler <itai.handler@gmail.com>
Cc: mwalle@kernel.org,  pratyush@kernel.org,
	 linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
	 vigneshr@ti.com,  richard@nod.at, takahiro.kuwano@infineon.com
Subject: Re: [PATCH v2 3/3] mtd: spi-nor: take the flash lock in spi_nor_remove()
Date: Mon, 14 Sep 2026 14:19:04 +0200	[thread overview]
Message-ID: <87a4pkowjr.fsf@bootlin.com> (raw)
In-Reply-To: <20260914081149.1916589-4-itai.handler@gmail.com> (Itai Handler's message of "Mon, 14 Sep 2026 11:11:49 +0300")

On 14/09/2026 at 11:11:49 +03, Itai Handler <itai.handler@gmail.com> wrote:

> spi_nor_remove() restores the addressing mode with the same unlocked
> call to spi_nor_restore() that spi_nor_shutdown() used before the
> previous patch, and it is exposed the same way: the MTD device is still
> registered at that point, so an unbind can run the restore while another
> thread is in the middle of an operation. A busy flash silently ignores
> the restore, and a restore that lands between two chunks of a read
> switches the chip to 3-byte addressing while the driver keeps sending
> 4 address bytes.
>
> Moving the restore after mtd_device_unregister() would not fix this.
> Since commit 19bfa9ebebb5 ("mtd: use refcount to prevent corruption")
> del_mtd_device() drops a reference instead of refusing with -EBUSY when
> the device is in use, so unregistering returns right away and does not
> wait for an operation that is already running.
>
> Take nor->lock for the restore, as spi_nor_shutdown() now does. The
> unregister stays unconditional, so a flash whose restore had to be
> skipped is still torn down.
>
> Fixes: 59b356ffd0b0 ("mtd: m25p80: restore the status of SPI flash when exiting")
> Signed-off-by: Itai Handler <itai.handler@gmail.com>
> ---
>  drivers/mtd/spi-nor/core.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 647bf8dce719..8d0302565445 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -3852,8 +3852,14 @@ static int spi_nor_probe(struct spi_mem *spimem)
>  static int spi_nor_remove(struct spi_mem *spimem)
>  {
>  	struct spi_nor *nor = spi_mem_get_drvdata(spimem);
> +	int ret;
>  
> -	spi_nor_restore(nor);
> +	/* As in spi_nor_shutdown(), do not restore under an operation. */
> +	ret = spi_nor_prep_and_lock(nor);
> +	if (!ret) {
> +		spi_nor_restore(nor);
> +		spi_nor_unlock_and_unprep(nor);
> +	}

Why isn't this folded into patch 2? You are fixing the same race, but
you do it in two steps which makes step 1 incomplete. I don't get it.

You are making things overly complicated for no reason. You commit logs
are overly verbose and the comments are also superfluous.

Thanks,
Miquèl

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