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Wed, 09 Mar 2022 11:35:47 -0800 (PST) X-Google-Smtp-Source: ABdhPJw0la76JJIHCiuuXGNz+2k1My92hBu1ArSVMN8GhFQj6QO8YhMJVj5DYkOvqpLnFDQ4NiVOIlnzHU+c6/gk5RQ= X-Received: by 2002:a05:6000:10c6:b0:1f1:e562:bee2 with SMTP id b6-20020a05600010c600b001f1e562bee2mr892423wrx.654.1646854547635; Wed, 09 Mar 2022 11:35:47 -0800 (PST) MIME-Version: 1.0 References: <20220309184238.1583093-1-agruenba@redhat.com> In-Reply-To: From: Andreas Gruenbacher Date: Wed, 9 Mar 2022 20:35:36 +0100 Message-ID: Subject: Re: Buffered I/O broken on s390x with page faults disabled (gfs2) To: Linus Torvalds Cc: Catalin Marinas , David Hildenbrand , Alexander Viro , linux-s390 , Linux-MM , linux-fsdevel , linux-btrfs X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 983F580015 X-Stat-Signature: s1c3q8c9jsc4n1rtosxkjqkbng3qoryy Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=iEtj32OT; spf=none (imf30.hostedemail.com: domain of agruenba@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=agruenba@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-HE-Tag: 1646854550-407642 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 8:22 PM Linus Torvalds wrote: > 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. Ouch, that was stupid. Same for the "return size". > 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). That's better, thanks. Andreas