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Date:   Mon, 22 Mar 2021 11:46:21 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Yu-cheng Yu <yu-cheng.yu@intel.com>, x86@kernel.org,
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Subject: Re: [PATCH v23 12/28] x86/mm: Update ptep_set_wrprotect() and
 pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW
Message-ID: <YFh1fabrBok74F8X@hirez.programming.kicks-ass.net>
References: <20210316151054.5405-1-yu-cheng.yu@intel.com>
 <20210316151054.5405-13-yu-cheng.yu@intel.com>
 <20210322101502.b5hdy3qgyh6hf3sr@box>
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On Mon, Mar 22, 2021 at 01:15:02PM +0300, Kirill A. Shutemov wrote:
> On Tue, Mar 16, 2021 at 08:10:38AM -0700, Yu-cheng Yu wrote:

> > +		pte_t old_pte, new_pte;
> > +
> > +		old_pte = READ_ONCE(*ptep);
> > +		do {
> > +			new_pte = pte_wrprotect(old_pte);
> > +		} while (!try_cmpxchg(&ptep->pte, &old_pte.pte, new_pte.pte));
> 
> I think this is wrong. You need to update old_pte on every loop iteration,
> otherwise you can get in to endless loop.

It is correct, please consider why the old argument is a pointer.