Re: [PATCH v3 1/1] mtd: spi-nor: core: Prevent oops during driver removal with active read or write operations

From: "Michael Walle" <mwalle@kernel.org>
To: "Romli, Khairul Anuar" <khairul.anuar.romli@altera.com>,
	"Tudor Ambarus" <tudor.ambarus@linaro.org>,
	"Pratyush Yadav" <pratyush@kernel.org>,
	"Miquel Raynal" <miquel.raynal@bootlin.com>,
	"Richard Weinberger" <richard@nod.at>,
	"Vignesh Raghavendra" <vigneshr@ti.com>,
	"open list:SPI NOR SUBSYSTEM" <linux-mtd@lists.infradead.org>,
	"open list" <linux-kernel@vger.kernel.org>,
	"Gerlach, Matthew" <matthew.gerlach@altera.com>
Subject: Re: [PATCH v3 1/1] mtd: spi-nor: core: Prevent oops during driver removal with active read or write operations
Date: Wed, 30 Jul 2025 09:50:07 +0200	[thread overview]
Message-ID: <DBP84FIUUQO7.369TFNTJFELMW@kernel.org> (raw)
In-Reply-To: < <MN2PR03MB49271E2D022D305BC149BA4FC624A@MN2PR03MB4927.namprd03.prod.outlook.com>

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Hi,

> > On Wed Jul 30, 2025 at 3:39 AM CEST, Khairul Anuar Romli wrote:
> > > From: kromli <khairul.anuar.romli@altera.com>
> > >
> > > Ensure that the pointer passed to module_put() in spi_nor_put_device()
> > > is not NULL before use. This change adds a guard clause to return
> > > early, preventing the kernel crash below when the cadence-qspi driver
> > > is removed during a dd operation:
> > 
> > As already asked in v2. This needs a (more detailed) description what is going
> > on and what is going wrong.
> > 
> > -michael
>
> Hi,
>
> We just run the following test we observe the crash. 
>
> time dd if=/dev/mtd1 of=out.img bs=1MB count=1000 &
> echo spi0.0 > /sys/bus/spi/drivers/spi-nor/unbind
> echo spi0.0 > /sys/bus/spi/drivers/spi-nor/bind
>
> From the observation, the dd is not entirely terminated when the unbind took place.
> Maybe there is other changes require to ensure the dd operation gets terminated 
> when driver unbind/remove.

I'd expect an analysis what's going wrong in the kernel to judge the
correctness of the patch.

Thanks,
-michael

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