Re: [PATCH] ALSA: ac97c: Fix an error handling path in 'atmel_ac97c_probe()'

[Julia Lawall]

On Thu, 31 Aug 2017, Alexandre Belloni wrote:

> Hi,
>
> On 31/08/2017 at 21:08:10 +0200, Christophe JAILLET wrote:
> > Le 31/08/2017 à 12:38, Mark Brown a écrit :
> > > On Thu, Aug 31, 2017 at 12:31:33PM +0200, Takashi Iwai wrote:
> > >
> > > > This is again a typical problem by such a trivial fix patch: the code
> > > > looks as if it were trivial and correct, buried in a patch series that
> > > > easily leads to the oversight by the maintainer's review.
> > > Right, plus the amount of context that diff shows you.
> > >
> > Hi,
> >
> > My proposed patch was initially triggered using coccinelle, as you must have
> > guessed.
> >
> > In fact, I was surprised by the initial commit.
> > I don't have any strong opinion if testing the return value of
> > 'clk_prepare_enable()' is relevant or not, but I was surprised that the
> > error handling path had not been updated at the same time.
> >
> > So, before posting my patch, I have searched a bit in git history and it
> > gave:
> >
> > git shortlog --author="Arvind Yadav" | grep clk_prepare
> >       ata: sata_rcar: Handle return value of clk_prepare_enable
> >       hwrng: omap3-rom - Handle return value of clk_prepare_enable
> >       crypto: img-hash - Handle return value of clk_prepare_enable
> >       dmaengine: DW DMAC: Handle return value of clk_prepare_enable
> >       gpio: davinci: Handle return value of clk_prepare_enable
> >       cpufreq: kirkwood-cpufreq:- Handle return value of
> > clk_prepare_enable()
> >       dmaengine: imx-sdma: Handle return value of clk_prepare_enable
> >       Input: s3c2410_ts - handle return value of clk_prepare_enable
> >       iio: adc: xilinx: Handle return value of clk_prepare_enable
> >       iio:adc:lpc32xx Handle return value of clk_prepare_enable
> >       memory: ti-aemif: Handle return value of clk_prepare_enable
> >       spi: davinci: Handle return value of clk_prepare_enable
> >       [media] tc358743: Handle return value of clk_prepare_enable
> >       mtd: nand: orion: Handle return value of clk_prepare_enable
> >       iio: Aspeed ADC - Handle return value of clk_prepare_enable
> >       PM / devfreq: exynos-nocp: Handle return value of clk_prepare_enable
> >       PM / devfreq: exynos-ppmu: Handle return value of clk_prepare_enable
> >       usb: host: ehci-exynos: Handle return value of clk_prepare_enable
> >       usb: mtu3: Handle return value of clk_prepare_enable
> >       usb: mtu3: Handle return value of clk_prepare_enable
> >       video: fbdev: pxafb: Handle return value of clk_prepare_enable
> >       usb: gadget: mv_udc: Handle return value of clk_prepare_enable.
> >       usb: dwc3: exynos: Handle return value of clk_prepare_enable
> >       i2c: at91: Handle return value of clk_prepare_enable
> >       i2c: emev2: Handle return value of clk_prepare_enable
> >       usb: host: ohci-pxa27x: Handle return value of clk_prepare_enable
> >       thermal: imx: Handle return value of clk_prepare_enable
> >       thermal: hisilicon: Handle return value of clk_prepare_enable
> >       PCI: rockchip: Check for clk_prepare_enable() errors during resume
> >       watchdog: meson: Handle return value of clk_prepare_enable
> >       watchdog: davinci: Handle return value of clk_prepare_enable
> >       mfd: tc6393xb: Handle return value of clk_prepare_enable
> >       ASoC: samsung: s3c2412: Handle return value of clk_prepare_enable.
> >       ASoC: samsung: s3c24xx: Handle return value of clk_prepare_enable.
> >       ASoC: samsung: pcm: Handle return value of clk_prepare_enable.
> >       ASoC: samsung: i2s: Handle return value of clk_prepare_enable.
> >       ASoC: samsung: spdif: Handle return value of clk_prepare_enable.
> >       ASoC: mxs-saif: Handle return value of clk_prepare_enable/clk_prepare.
> >       ASoC: jz4740: Handle return value of clk_prepare_enable.
> >       ASoC: sun4i-spdif: Handle return value of clk_prepare_enable.
> >       ASoC: atmel: ac97c: Handle return value of clk_prepare_enable.
> >       gpio: mb86s7x: Handle return value of clk_prepare_enable.
> >       memory: mtk-smi: Handle return value of clk_prepare_enable
> >       mmc: sdhci-st: Handle return value of clk_prepare_enable
> >       mmc: wmt-sdmmc: Handle return value of clk_prepare_enable
> >       mmc: mxcmmc: Handle return value of clk_prepare_enable
> >       dmaengine: at_xdmac: Handle return value of clk_prepare_enable.
> >       mtd: nand: denali: Handle return value of clk_prepare_enable.
> >       mtd: oxnas_nand: Handle clk_prepare_enable/clk_disable_unprepare.
> >       mtd: nand: lpc32xx_slc: Handle return value of clk_prepare_enable.
> >       mtd: nand: lpc32xx_mlc: Handle return value of clk_prepare_enable.
> >       mtd: st_spi_fsm: Handle clk_prepare_enable/clk_disable_unprepare.
> >
> > Some of these are after a devm_clk_get(), which does not require a
> > modification in the error handling path (at least according to the one I've
> > looked at)
> >
> > Some don't have any [devm_]clk_get() in the same function, and were not
> > investigated further.
> >
> > But several also had the same construction as the one reported in this
> > thread, and needed, IMHO, an update of the error handling path to call
> > through clk_put().
> >
> >
> > It was "too" surprising to me to have "all" these "obviously" incomplete
> > patches merged.
> > I thought that I had missed something obvious and decided to propose one fix
> > to see the reaction (and didn't expected all your replies!)
> >
>
> You didn't miss anything, that's exactly what I am complaining about
> some of the patches were OK, some aren't and all the real work is left
> to the maintainer.

The commit message is also a bit strange:

clk_prepare_enable() and clk_prepare() can fail here and
we must check its return value.

When someone in the future is tring to understand whether or nor calls to
clk_prepare_enable can fail, it would be misleading to have "can fail" and
"we must check" in the history of a context where failure is not possible.

julia


>
> > So now, I think we should go through the commits above to either revert the
> > commit and remove the test (and document why it is not needed) or fix the
> > error handling path accordingly, even if one could know that it cant'
> > happen.
>
> I think you should go ahead and fix those now...
>
> --
> Alexandre Belloni, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com
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