Re: [Xen-devel] [PATCH] arm: Coverity 1469342 correct find_*_bit() functions use

[Julien Grall <julien.grall@xxxxxxx>]

On 24/05/18 15:07, Artem Mygaiev wrote:
> Hi Julien
Hi Artem,

> On 24.05.18 16:49, Julien Grall wrote:
> > Hi Artem,
> >
> > Thank you for the report.
> >
> > On 24/05/18 14:20, Artem Mygaiev wrote:
> > > vgic_vcpu_pending_irq() uses find_next_bit() library function with 
> > > single 'unsigned long' variable, while it is designed to work with 
> > > memory regions. Nothing wrong is happening since 'offset' is set to 0 
> > > (other values could lead to memory corruption), but it would be more 
> > > correct to use the find_first_bit() function instead.
> > I don't understand the commit message. It is fine to use other offset 
> > than 0 in find_next_bit as long as it is smaller than 32. There would 
> > be no corruption happening.
> > Furthermore, find_first_bit(&apr, 32, 0) and find_next_bit(&apr, 32) 
> > are equivalent because the former is just a macro using the latter 
> > (see include/asm-arm/arm64/bitops.h).
> > So as it is the patch is not solving anything. However, I think this 
> > is just a false positive. Coverity should be able to guess that it 
> > will not go past the array (BITOP_WORD will turned into 0).
> Absolutely agree with you. Probably my message was not clear enough - 
> with this particular patch I am not trying to fix a memory corruption, 
> there is no memory corruption in the code now. It is just the use of 
> functions: find_first_bit() is a better fit since the 
> vgic_vcpu_pending_irq() function does not need to go over memory region 
> and checks only one 32-bit variable. I have mentioned Coverity issue 
> here because this was a false positive detected after today's test run.
Feel free to resend this patch as a clean-up. I always found the use of 
find_next_bit confusing over find_first_bit.
However, I don't think coverity should be mention in the commit message 
or title. This is making thing very confusing as, IHMO, this is a false 
positive. We tend to only mention coverity when this is either going to 
silent coverity or fix the defect.
Cheers,

--
Julien Grall

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