From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751875AbdLNAdX (ORCPT ); Wed, 13 Dec 2017 19:33:23 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:33503 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750749AbdLNAdV (ORCPT ); Wed, 13 Dec 2017 19:33:21 -0500 X-Google-Smtp-Source: ACJfBotCVfYGXEm1VgGh6ijeZiLgdHcVPNSh0ELaPIsWKVF8xlCBfkfLzSp0btbH+aWf1Fmw3HZZ3Q== Date: Thu, 14 Dec 2017 03:33:18 +0300 From: "Kirill A. Shutemov" To: Andrew Morton Cc: "Kirill A. Shutemov" , Vlastimil Babka , Andrea Arcangeli , Michal Hocko , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ingo Molnar , "H . Peter Anvin" , Thomas Gleixner Subject: Re: [PATCHv4 09/12] x86/mm: Provide pmdp_establish() helper Message-ID: <20171214003318.xli42qgybplln754@node.shutemov.name> References: <20171213105756.69879-1-kirill.shutemov@linux.intel.com> <20171213105756.69879-10-kirill.shutemov@linux.intel.com> <20171213160951.249071f2aecdccb38b6bb646@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171213160951.249071f2aecdccb38b6bb646@linux-foundation.org> User-Agent: NeoMutt/20171208 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 13, 2017 at 04:09:51PM -0800, Andrew Morton wrote: > > @@ -181,6 +182,40 @@ static inline pmd_t native_pmdp_get_and_clear(pmd_t *pmdp) > > #define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp) > > #endif > > > > +#ifndef pmdp_establish > > +#define pmdp_establish pmdp_establish > > +static inline pmd_t pmdp_establish(struct vm_area_struct *vma, > > + unsigned long address, pmd_t *pmdp, pmd_t pmd) > > +{ > > + pmd_t old; > > + > > + /* > > + * If pmd has present bit cleared we can get away without expensive > > + * cmpxchg64: we can update pmdp half-by-half without racing with > > + * anybody. > > + */ > > + if (!(pmd_val(pmd) & _PAGE_PRESENT)) { > > + union split_pmd old, new, *ptr; > > + > > + ptr = (union split_pmd *)pmdp; > > + > > + new.pmd = pmd; > > + > > + /* xchg acts as a barrier before setting of the high bits */ > > + old.pmd_low = xchg(&ptr->pmd_low, new.pmd_low); > > + old.pmd_high = ptr->pmd_high; > > + ptr->pmd_high = new.pmd_high; > > + return old.pmd; > > + } > > + > > + { > > + old = *pmdp; > > + } while (cmpxchg64(&pmdp->pmd, old.pmd, pmd.pmd) != old.pmd); > > um, what happened here? Ouch.. Yeah, we need 'do' here. :-/ Apparently, it's a valid C code that would run the body once and it worked for me because I didn't hit the race condition. -- Kirill A. Shutemov