linux-kernel - Re: [PATCH V2] staging: gpib: Remove a dead condition in if statement

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Message-ID: <CAEO-vhFAb=xfc2sZiezW7Zn0dWNQ4axVxE6GErayKs76NtG1bg@mail.gmail.com>
Date: Wed, 16 Oct 2024 20:47:21 -0600
From: "Everest K.C." <everestkc@...restkc.com.np>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Greg KH <gregkh@...uxfoundation.org>, dpenkler@...il.com, 
	skhan@...uxfoundation.org, linux-staging@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] staging: gpib: Remove a dead condition in if statement

On Wed, Oct 16, 2024 at 9:00 AM Dan Carpenter <dan.carpenter@...aro.org> wrote:
>
> On Wed, Oct 16, 2024 at 06:54:00AM -0600, Everest K.C. wrote:
> > > > 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))
> > >
> > > No, this is incorrect, now we never notice is the call to
> > > fluke_get_dma_residue() has failed.  Please fix that bug instead (hint,
> > > Covertity is giving you a pointer to where something might be wrong, but
> > > this change is NOT how to fix it.)
> > I need a little guidance here.
> > My best guess to fix the bug would be to make fluke_get_dma_residue()
> > return an int instead of unsigned int or size_t. But theoretically the
> > maximum value of residue can be UINT_MAX, and casting it to int will
> > result in a negative number, which in turn will cause  the error check
> > condition to evaluate to true.
> > The best solution I see would be to make fluke_get_dma_residue() return
> > an int (-1 for error and 0 for success). Then pass the address of residue
> > reference to fluke_get_dma_residue() to be updated.
> > Am I on the right track ?
>
> Functions shouldn't return -1 on error, they should return proper error codes.
Noted.
> >
> > Also,I searched for the functions with names that match get_dma_residue
> > in the kernel source code and found that they return unsigned int. I also
> > noticed that no error checks have been made to check if get_dma_residue
> > was successful.
>
> $ git grep get_dma_residue | grep static | grep -v gpib
>
> arch/alpha/include/asm/dma.h:static __inline__ int get_dma_residue(unsigned int dmanr)
> arch/arm/mach-footbridge/dma-isa.c:static int isa_get_dma_residue(unsigned int chan, dma_t *dma)
> arch/m68k/include/asm/floppy.h:static int vdma_get_dma_residue(unsigned int dummy)
> arch/mips/include/asm/dma.h:static __inline__ int get_dma_residue(unsigned int dmanr)
> arch/mips/include/asm/mach-au1x00/au1000_dma.h:static inline int get_dma_residue(unsigned int dmanr)
> arch/mips/include/asm/mach-generic/floppy.h:static inline int fd_get_dma_residue(void)
> arch/mips/include/asm/mach-jazz/floppy.h:static inline int fd_get_dma_residue(void)
> arch/parisc/include/asm/dma.h:static __inline__ int get_dma_residue(unsigned int dmanr)
> arch/parisc/include/asm/floppy.h:static int vdma_get_dma_residue(unsigned int dummy)
> arch/powerpc/include/asm/dma.h:static __inline__ int get_dma_residue(unsigned int dmanr)
> arch/powerpc/include/asm/floppy.h:static int vdma_get_dma_residue(unsigned int dummy)
> arch/sh/drivers/dma/dma-pvr2.c:static int pvr2_get_dma_residue(struct dma_channel *chan)
> arch/sh/drivers/dma/dma-sh.c:static int sh_dmac_get_dma_residue(struct dma_channel *chan)
> arch/sparc/include/asm/floppy_64.h:static unsigned int sun_get_dma_residue(void)
> arch/sparc/include/asm/floppy_64.h:static unsigned int sun_pci_get_dma_residue(void)
> arch/sparc/include/asm/parport_64.h:static inline unsigned int get_dma_residue(unsigned int dmanr)
> arch/x86/include/asm/dma.h:static inline int get_dma_residue(unsigned int dmanr)
> arch/x86/include/asm/floppy.h:static int vdma_get_dma_residue(unsigned int dummy)
>
> Only the Sparc functions return unsigned int.  The rest return int.
Why is it so ? Are there any resources I could go through to
understand it better?
> The return value is going to be between 0 and priv->dma_buffer_size (0x7ff).
> It's set in fluke_allocate_private().
Thank you for pointing it out.
> Just make the return value an int.
Noted.

> regards,
> dan carpenter
Thanks,
Everest K.C.