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[195.135.220.15]) by mx.google.com with ESMTPS id y21si3318817edd.139.2019.03.27.06.15.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Mar 2019 06:15:08 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 7D0A9AFD1; Wed, 27 Mar 2019 13:15:07 +0000 (UTC) Date: Wed, 27 Mar 2019 14:15:06 +0100 From: Michal Hocko To: Anshuman Khandual Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, hannes@cmpxchg.org, david@redhat.com, vbabka@suse.cz, willy@infradead.org, akpm@linux-foundation.org, Nicholas Piggin Subject: Re: [PATCH] mm/page-flags: Check enforce parameter in PF_ONLY_HEAD() Message-ID: <20190327131506.GI11927@dhcp22.suse.cz> References: <1553689672-28343-1-git-send-email-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1553689672-28343-1-git-send-email-anshuman.khandual@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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: [Cc Nick] On Wed 27-03-19 17:57:52, Anshuman Khandual wrote: > Just check for enforce parameter in PF_ONLY_HEAD() wrapper before calling > VM_BUG_ON_PGFLAGS() for tail pages. Why is this an actual fix? Only TESTPAGEFLAG doesn't enforce the check but I suspect that Nick just wanted the check to be _always_ performed as the name suggests. What kind of problem are you trying to solve? > Fixes: 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit") > Signed-off-by: Anshuman Khandual > --- > include/linux/page-flags.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 9f8712a4b1a5..82539e287bc6 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -229,7 +229,7 @@ static inline void page_init_poison(struct page *page, size_t size) > #define PF_ANY(page, enforce) PF_POISONED_CHECK(page) > #define PF_HEAD(page, enforce) PF_POISONED_CHECK(compound_head(page)) > #define PF_ONLY_HEAD(page, enforce) ({ \ > - VM_BUG_ON_PGFLAGS(PageTail(page), page); \ > + VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page); \ > PF_POISONED_CHECK(page); }) > #define PF_NO_TAIL(page, enforce) ({ \ > VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page); \ > -- > 2.20.1 > -- Michal Hocko SUSE Labs