Re: [PATCH 1/1] ipc/shm: fix the historical/wrong mm->start_stack check

From: Hugh Dickins
Date: Mon Aug 25 2014 - 14:53:39 EST

On Mon, 25 Aug 2014, Oleg Nesterov wrote:
> On 08/25, Hugh Dickins wrote:
> > And I think I'll let Linus's guard page justify your 4 (to match comment)
> > in place of the original's mysterious 5.
> Ah, thanks again. Yes, if we want to guarantee 4 pages we should check 5.
> Although obviously this doesn't explain the original's 5, this was
> written before check_stack_guard_page().

I meant, you changed the coded 5 to 4, to match the comment above it;
and if I were insistent on maximizing back-compatible-safety, I would
say that 4 should go back to 5; but since Linus added the guard page
gap at next->vm_start in between, I don't mind if you stick with 4
there to match the comment.

Disclaimer: I may be mistaken in each clause of that paragraph,
and you may prefer to ignore everything I wrote there as worthless!
But I didn't understand your "to guarantee 4 we should check 5".

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