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[209.85.167.169]) by smtp.gmail.com with ESMTPSA id k15-20020a056808068f00b002d91362e56esm1338236oig.1.2022.03.09.11.22.02 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Mar 2022 11:22:03 -0800 (PST) Received: by mail-oi1-f169.google.com with SMTP id q189so3658591oia.9 for ; Wed, 09 Mar 2022 11:22:02 -0800 (PST) X-Received: by 2002:a05:6808:2209:b0:2d5:1bb4:bb37 with SMTP id bd9-20020a056808220900b002d51bb4bb37mr702760oib.53.1646853722554; Wed, 09 Mar 2022 11:22:02 -0800 (PST) MIME-Version: 1.0 References: <20220309184238.1583093-1-agruenba@redhat.com> In-Reply-To: <20220309184238.1583093-1-agruenba@redhat.com> From: Linus Torvalds Date: Wed, 9 Mar 2022 11:21:43 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Buffered I/O broken on s390x with page faults disabled (gfs2) To: Andreas Gruenbacher Cc: Catalin Marinas , David Hildenbrand , Alexander Viro , linux-s390 , Linux-MM , linux-fsdevel , linux-btrfs Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 8BED414000B X-Stat-Signature: qqdd5z9x1d83jj4yuj4er43b8tdgmziu X-Rspam-User: Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=Cuk6Sng0; spf=pass (imf23.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.167.179 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-Rspamd-Server: rspam07 X-HE-Tag: 1646853726-249451 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 Wed, Mar 9, 2022 at 10:42 AM Andreas Gruenbacher wrote: > > + while (start != end) { > + if (fixup_user_fault(mm, start, fault_flags, NULL)) > + goto out; > + start += PAGE_SIZE; > + } > + mmap_read_unlock(mm); > + > +out: > + if (size > (unsigned long)uaddr - start) > + return size - ((unsigned long)uaddr - start); > + return 0; > } What? That "goto out" is completely broken. It explicitly avoids the "mmap_read_unlock()" for some reason I can't for the life of me understand. You must have done that on purpose, since a simple "break" would have been the sane and simple thing to do, but it looks *entirely* wrong to me. I think the whole loop should just be mmap_read_lock(mm); do { if (fixup_user_fault(mm, start, fault_flags, NULL)) break; start = (start + PAGE_SIZE) & PAGE_MASK; } while (start != end); mmap_read_unlock(mm); which also doesn't need that first unlooped iteration (not that I think that passing in the non-masked starting address for the first case actually helps, but that's a different thing). Linus