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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 126-20020a4a0384000000b00480816a5b8csm1075684ooi.18.2022.10.27.18.32.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Oct 2022 18:32:10 -0700 (PDT) Date: Thu, 27 Oct 2022 18:32:01 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Peter Xu cc: Hugh Dickins , Yuanzheng Song , akpm@linux-foundation.org, gregkh@linuxfoundation.org, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH STABLE 5.10] mm/memory: add non-anonymous page check in the copy_present_page() In-Reply-To: Message-ID: <432c4428-b6d4-f93-266-b920a854c3c@google.com> References: <20221024094911.3054769-1-songyuanzheng@huawei.com> <3823471f-6dda-256e-e082-718879c05449@google.com> <8aad435-bdc6-816f-2fe4-efe53abd6e5@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666920732; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=331LzS+zCTF3pctjI7hxcWQiOyXx0a+a6N3w5ukhHUE=; b=NUruTEylfYS8HMHYs2n+h8xzeSFCPJLnhXiR6zQkPNRcCLOf49SUdR9fiJiBjMb8HEW3vv NMTZu+mQD0pkyKgOcZSooKEgOlonOyRjXCsaS4wiFFBDmpBHyX2Qgp9mqnb9q6bsb7KwXx 3Uhqy6ES+60pwxhxOsDZTZXOu6nzcpY= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=kgs6Xv0q; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf16.hostedemail.com: domain of hughd@google.com designates 209.85.161.51 as permitted sender) smtp.mailfrom=hughd@google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666920732; a=rsa-sha256; cv=none; b=2Beh8rhdyoVZcjhw9gqPbBYGHBjqB91mgzjurNPw2FfHSJj/oJkgi4SHy8/1Vic/EjWPyO jnqexC/nk5SoOMlVbPObskU7Aib5rzFnn+lf1EeMgc2x6ZhbfOt1NF+6i2qgJCr9eu6miR Zp186cSlakRPmi1VkxqFvY09+eeej4w= X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 71FFF180002 X-Rspam-User: Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=kgs6Xv0q; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf16.hostedemail.com: domain of hughd@google.com designates 209.85.161.51 as permitted sender) smtp.mailfrom=hughd@google.com X-Stat-Signature: 6k19b8p3x37w5gtm9eq6q6mjw93wi3t5 X-HE-Tag: 1666920732-782741 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: Reinstating Cc stable, which I removed just before the discussion settled. On Thu, 27 Oct 2022, Peter Xu wrote: > ... > > After a re-read and 2nd thought, I think David has a valid point in that we > shouldn't have special handling of !anon pages on CoW during fork(), > because that seems to be against the fundamental concept of fork(). > > So now I think I agree the !Anon original check does look a bit cleaner, > and also make fork() behavior matching with the old/new kernels, irrelevant > of the pin mess. Thanks Peter. So Yuanzheng's patch for 5.10 is exactly right. Sorry for leading everyone astray: my mistake was to suppose that its !PageAnon check was simply to avoid the later BUG_ON(!anon_vma): whereas David and Peter now agree that it actually corrects the semantics for fork() on file pages. I lift my hold on Yuanzheng's patch: nobody actually said "Acked-by", but I think the discussion and resolution have given better than that. (No 3rd thoughts please!) Hugh