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[209.85.167.53]) by smtp.gmail.com with ESMTPSA id l21sm39008lja.35.2021.01.05.13.23.05 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Jan 2021 13:23:05 -0800 (PST) Received: by mail-lf1-f53.google.com with SMTP id h22so1889694lfu.2 for ; Tue, 05 Jan 2021 13:23:05 -0800 (PST) X-Received: by 2002:a05:6512:789:: with SMTP id x9mr461400lfr.487.1609881785021; Tue, 05 Jan 2021 13:23:05 -0800 (PST) MIME-Version: 1.0 References: <000000000000886dbd05b7ffa8db@google.com> <20210104124153.0992b1f7fd1a145e193a333f@linux-foundation.org> In-Reply-To: From: Linus Torvalds Date: Tue, 5 Jan 2021 13:22:49 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: kernel BUG at mm/page-writeback.c:LINE! To: Hugh Dickins Cc: Andrew Morton , Matthew Wilcox , syzbot , Linux Kernel Mailing List , Linux-MM , syzkaller-bugs Content-Type: text/plain; charset="UTF-8" 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 Tue, Jan 5, 2021 at 1:13 PM Hugh Dickins wrote: > > I was going to raise a question, whether you should now revert > 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and BUG_ON(PageWriteback)"): > which would not have gone in like that if c2407cf7d22d were already in. Honestly, even if it wasn't for that PageTail issue, I think 073861ed77b6 is just the right thing to do anyway. It just feels _so_ much safer to not have the possibility of that page wait thing following while the page is possibly then being free'd and re-used at the same time. So I think the only reason to revert that commit would be if we were to find that it's a huge performance problem to raise the page refcount temporarily. Which I think is very unlikely (since we already dirty the page structure due to the page flags modification - although they are far enough apart that it might be a different cacheline). Linus