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[209.85.167.51]) by smtp.gmail.com with ESMTPSA id h7-20020a19ca47000000b0044829144111sm1876626lfj.26.2022.03.08.09.40.32 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Mar 2022 09:40:32 -0800 (PST) Received: by mail-lf1-f51.google.com with SMTP id h14so8569767lfk.11 for ; Tue, 08 Mar 2022 09:40:32 -0800 (PST) X-Received: by 2002:a19:e048:0:b0:448:2caa:7ed2 with SMTP id g8-20020a19e048000000b004482caa7ed2mr8519640lfj.449.1646761232492; Tue, 08 Mar 2022 09:40:32 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Tue, 8 Mar 2022 09:40:16 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Buffered I/O broken on s390x with page faults disabled (gfs2) To: David Hildenbrand Cc: Andreas Gruenbacher , Alexander Viro , linux-s390 , Linux-MM , linux-fsdevel , linux-btrfs Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 597791C0004 X-Stat-Signature: 4pkdg8ijd4okcrrkc6cmk1xksx5n1ncz Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=XUxN+P64; spf=pass (imf18.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.167.49 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-HE-Tag: 1646761238-246539 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, Mar 8, 2022 at 9:26 AM Linus Torvalds wrote: > > Your actual patch looks pretty nasty, though. We avoid marking it > accessed on purpose (to avoid atomicity issues wrt hw-dirty bits etc), > but still, that patch makes me go "there has to be a better way". That better way might be to make q() not use GUP at all. It doesn't want the page - it just wants to make sure the fault is handled. For the fault_in_readable() case we already just do the user access. The only reason we don't do that for fault_in_safe_writeable() is that we don't have a good non-destructive user write. Hmm. The futex code actually uses "fixup_user_fault()" for this case. Maybe fault_in_safe_writeable() should do that? Linus