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From: "Arnd Bergmann" <arnd@arndb.de>
To: "Christian Marangi" <ansuelsmth@gmail.com>,
	"Manivannan Sadhasivam" <mani@kernel.org>,
	"Miquel Raynal" <miquel.raynal@bootlin.com>,
	"Richard Weinberger" <richard@nod.at>,
	"Vignesh Raghavendra" <vigneshr@ti.com>,
	"Vinod Koul" <vkoul@kernel.org>,
	"Mark Brown" <broonie@kernel.org>,
	linux-mtd@lists.infradead.org, linux-arm-msm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Subject: Re: [PATCH] mtd: nand: raw: qcom_nandc: handle error pointer from adm prep_slave_sg
Date: Fri, 16 Sep 2022 11:01:11 +0200	[thread overview]
Message-ID: <4dcb0e76-b965-42da-b637-751d2f8e1c51@www.fastmail.com> (raw)
In-Reply-To: <20220916001038.11147-1-ansuelsmth@gmail.com>

On Fri, Sep 16, 2022, at 2:10 AM, Christian Marangi wrote:
> ADM dma engine has changed to also provide error pointer instaed of
> plain NULL pointer on invalid configuration of prep_slave_sg function.
> Currently this is not handled and an error pointer is detected as a
> valid dma_desc. This cause kernel panic as the driver doesn't fail
> with an invalid dma engine configuration.
>
> Correctly handle this case by checking if dma_desc is NULL or IS_ERR.

Using IS_ERR_OR_NULL() is almost never a correct solution. I think
in this case the problem is the adm_prep_slave_sg() function
that returns an invalid error code.

While error pointers are often better than NULL pointers for
passing information to the caller, a driver can't just change
the calling conventions on its own. If we want to change
the dmaengine_prep_slave_sg() API, I would suggest coming
up with a new name for a replacement interface that uses
error pointers instead of NULL first, and then changing
all callers to the new interface.

       Arnd

WARNING: multiple messages have this Message-ID (diff)
From: "Arnd Bergmann" <arnd@arndb.de>
To: "Christian Marangi" <ansuelsmth@gmail.com>,
	"Manivannan Sadhasivam" <mani@kernel.org>,
	"Miquel Raynal" <miquel.raynal@bootlin.com>,
	"Richard Weinberger" <richard@nod.at>,
	"Vignesh Raghavendra" <vigneshr@ti.com>,
	"Vinod Koul" <vkoul@kernel.org>,
	"Mark Brown" <broonie@kernel.org>,
	linux-mtd@lists.infradead.org, linux-arm-msm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Subject: Re: [PATCH] mtd: nand: raw: qcom_nandc: handle error pointer from adm prep_slave_sg
Date: Fri, 16 Sep 2022 11:01:11 +0200	[thread overview]
Message-ID: <4dcb0e76-b965-42da-b637-751d2f8e1c51@www.fastmail.com> (raw)
In-Reply-To: <20220916001038.11147-1-ansuelsmth@gmail.com>

On Fri, Sep 16, 2022, at 2:10 AM, Christian Marangi wrote:
> ADM dma engine has changed to also provide error pointer instaed of
> plain NULL pointer on invalid configuration of prep_slave_sg function.
> Currently this is not handled and an error pointer is detected as a
> valid dma_desc. This cause kernel panic as the driver doesn't fail
> with an invalid dma engine configuration.
>
> Correctly handle this case by checking if dma_desc is NULL or IS_ERR.

Using IS_ERR_OR_NULL() is almost never a correct solution. I think
in this case the problem is the adm_prep_slave_sg() function
that returns an invalid error code.

While error pointers are often better than NULL pointers for
passing information to the caller, a driver can't just change
the calling conventions on its own. If we want to change
the dmaengine_prep_slave_sg() API, I would suggest coming
up with a new name for a replacement interface that uses
error pointers instead of NULL first, and then changing
all callers to the new interface.

       Arnd

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

  reply	other threads:[~2022-09-16  9:10 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-16  0:10 [PATCH] mtd: nand: raw: qcom_nandc: handle error pointer from adm prep_slave_sg Christian Marangi
2022-09-16  0:10 ` Christian Marangi
2022-09-16  9:01 ` Arnd Bergmann [this message]
2022-09-16  9:01   ` Arnd Bergmann
2022-09-16  3:11   ` Christian Marangi
2022-09-16  3:11     ` Christian Marangi
2022-09-16 11:45     ` Arnd Bergmann
2022-09-16 11:45       ` Arnd Bergmann
2022-09-16  4:11       ` Christian Marangi
2022-09-16  4:11         ` Christian Marangi

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