Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751271AbdH1Gqh (ORCPT ); Mon, 28 Aug 2017 02:46:37 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:54864 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750830AbdH1Gqf (ORCPT ); Mon, 28 Aug 2017 02:46:35 -0400 Date: Mon, 28 Aug 2017 07:46:33 +0100 From: Al Viro To: Nicolas Pitre Cc: linux-fsdevel@vger.kernel.org, linux-embedded@vger.kernel.org, linux-kernel@vger.kernel.org, Chris Brandt Subject: Re: [PATCH v2 4/5] cramfs: add mmap support Message-ID: <20170828064632.GA26136@ZenIV.linux.org.uk> References: <20170816173536.1879-1-nicolas.pitre@linaro.org> <20170816173536.1879-5-nicolas.pitre@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170816173536.1879-5-nicolas.pitre@linaro.org> User-Agent: Mutt/1.8.3 (2017-05-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1655 Lines: 43 On Wed, Aug 16, 2017 at 01:35:35PM -0400, Nicolas Pitre wrote: > +static const struct vm_operations_struct cramfs_vmasplit_ops; > +static int cramfs_vmasplit_fault(struct vm_fault *vmf) > +{ > + struct mm_struct *mm = vmf->vma->vm_mm; > + struct vm_area_struct *vma, *new_vma; > + unsigned long split_val, split_addr; > + unsigned int split_pgoff, split_page; > + int ret; > + > + /* Retrieve the vma split address and validate it */ > + vma = vmf->vma; > + split_val = (unsigned long)vma->vm_private_data; > + split_pgoff = split_val & 0xffff; > + split_page = split_val >> 16; > + split_addr = vma->vm_start + split_page * PAGE_SIZE; > + pr_debug("fault: addr=%#lx vma=%#lx-%#lx split=%#lx\n", > + vmf->address, vma->vm_start, vma->vm_end, split_addr); > + if (!split_val || split_addr >= vma->vm_end || vmf->address < split_addr) > + return VM_FAULT_SIGSEGV; > + > + /* We have some vma surgery to do and need the write lock. */ > + up_read(&mm->mmap_sem); > + if (down_write_killable(&mm->mmap_sem)) > + return VM_FAULT_RETRY; > + > + /* Make sure the vma didn't change between the locks */ > + vma = find_vma(mm, vmf->address); > + if (vma->vm_ops != &cramfs_vmasplit_ops) { > + /* > + * Someone else raced with us and could have handled the fault. > + * Let it go back to user space and fault again if necessary. > + */ > + downgrade_write(&mm->mmap_sem); > + return VM_FAULT_NOPAGE; > + } > + > + /* Split the vma between the directly mapped area and the rest */ > + ret = split_vma(mm, vma, split_addr, 0); Egads... Everything else aside, who said that your split_... will have anything to do with the vma you get from find_vma()?