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Shutemov" To: Peter Zijlstra Cc: Yu-cheng Yu , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu , Haitao Huang 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: <20210322113849.snfoxcijpwoks4go@box> References: <20210316151054.5405-1-yu-cheng.yu@intel.com> <20210316151054.5405-13-yu-cheng.yu@intel.com> <20210322101502.b5hdy3qgyh6hf3sr@box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: F0D5980192DA X-Stat-Signature: pd9jitij84a67qiqehgx4rp7kzrqw4sb Received-SPF: none (shutemov.name>: No applicable sender policy available) receiver=imf16; identity=mailfrom; envelope-from=""; helo=mail-lj1-f173.google.com; client-ip=209.85.208.173 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616413123-186283 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Mar 22, 2021 at 11:46:21AM +0100, Peter Zijlstra wrote: > 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. Ah, right. Sorry for the noise. -- Kirill A. Shutemov