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SubjectRe: [PATCH] MIPS: Fix incorrect NULL check in local_flush_tlb_page()
Hello Jonas,

On Fri, Jul 04, 2014 at 11:52:51PM +0200, Jonas Gorski wrote:
> On Fri, Jul 4, 2014 at 7:07 PM, Emil Goode <emilgoode@gmail.com> wrote:
> > We check that the struct vm_area_struct pointer vma is NULL and
> > then dereference it. The intent must have been to check that
> > vma is not NULL before we dereference it in the next condition.
>
> Actually if it is NULL, then it will short-cut and won't dereference
> it (because !vma is true it can never become false again), so the
> condition would be fine previously.
>
> But, looking at the code a few lines into branch:
>
> if (!vma || cpu_context(cpu, vma->vm_mm) != 0) {
> unsigned long flags;
> int oldpid, newpid, idx;
>
> #ifdef DEBUG_TLB
> printk("[tlbpage<%lu,0x%08lx>]", cpu_context(cpu,
> vma->vm_mm), page);
> #endif
> newpid = cpu_context(cpu, vma->vm_mm) & ASID_MASK;
>
> it will be then dereferenced here, so the change is actually sensible,
> even if the description isn't quite spot-on where it breaks.

Sorry, this is what I meant but failed to explain clearly.

Perhaps the following is a bit better?

We check that the struct vm_area_struct pointer vma is NULL and then
dereference it a few lines below. The intent must have been to make sure
that vma is not NULL and then to check the value from cpu_context() for the
condition to be true.

Best regards,

Emil Goode


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