linux-kernel - Re: [PATCH] staging: gpib: Remove a dead condition in if statement

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Message-ID: <CAEO-vhEPmPSSb_T2b17KDjuvXCTvr41_JRK0tCBSqustMHjuxw@mail.gmail.com>
Date: Tue, 15 Oct 2024 17:50:00 -0600
From: "Everest K.C." <everestkc@...restkc.com.np>
To: Shuah Khan <skhan@...uxfoundation.org>
Cc: dpenkler@...il.com, gregkh@...uxfoundation.org, 
	linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: gpib: Remove a dead condition in if statement

On Tue, Oct 15, 2024 at 4:47 PM Shuah Khan <skhan@...uxfoundation.org> wrote:
>
> On 10/15/24 14:06, Everest K.C. wrote:
> > The variable `residue` is an unsigned int, also the function
> > `fluke_get_dma_residue` returns an unsigned int. The value of
> > an unsigned int can only be 0 at minimum.
> > The less-than-zero comparision can never be true.
> > Fix it by removing the dead condition in the if statement.
> >
> > This issue was reported by Coverity Scan.
> > Report:
> > CID 1600782: (#1 of 1): Macro compares unsigned to 0 (NO_EFFECT)
> > unsigned_compare: This less-than-zero comparison of an unsigned value
> > is never true. residue < 0U.
> >
> > Fixes: 55936779f496 ("staging: gpib: Add Fluke cda based cards GPIB driver")
> > Signed-off-by: Everest K.C. <everestkc@...restkc.com.np>
> > ---
> >   drivers/staging/gpib/eastwood/fluke_gpib.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/gpib/eastwood/fluke_gpib.c b/drivers/staging/gpib/eastwood/fluke_gpib.c
> > index f9f149db222d..51b4f9891a34 100644
> > --- a/drivers/staging/gpib/eastwood/fluke_gpib.c
> > +++ b/drivers/staging/gpib/eastwood/fluke_gpib.c
> > @@ -644,7 +644,7 @@ static int fluke_dma_read(gpib_board_t *board, uint8_t *buffer,
> >        */
> >       usleep_range(10, 15);
> >       residue = fluke_get_dma_residue(e_priv->dma_channel, dma_cookie);
> > -     if (WARN_ON_ONCE(residue > length || residue < 0))
> > +     if (WARN_ON_ONCE(residue > length))
>
> Are you sure this is the right fix? length is size_t
> fluke_get_dma_residue() returns unsigned int - yes
> the coverity report is correct, but should fluke_get_dma_residue()
> return size_t?
I agree that it looks kind of inconsistent. The variable residue returned
by fluke_get_dma_residue() is defined in a u32 defined in struct dma_tx_state.
I will wait for the feedback from the maintainers on this.
> >               return -EFAULT;
> >       *bytes_read += length - residue;
>
> bytes_read is also size_t
>
> >       dmaengine_terminate_all(e_priv->dma_channel);
>
> The patch should indicate it is against next. [PATCH next].
The patch was created from linux staging.
> thanks,
> -- Shuah
>
>
Thanks,
Everest K.C.