From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f175.google.com (mail-lb0-f175.google.com [209.85.217.175]) by kanga.kvack.org (Postfix) with ESMTP id B4B656B0069 for ; Thu, 16 Oct 2014 04:58:55 -0400 (EDT) Received: by mail-lb0-f175.google.com with SMTP id u10so2405843lbd.20 for ; Thu, 16 Oct 2014 01:58:54 -0700 (PDT) Received: from mail.efficios.com (mail.efficios.com. [78.47.125.74]) by mx.google.com with ESMTP id b11si33660673lbq.121.2014.10.16.01.58.53 for ; Thu, 16 Oct 2014 01:58:54 -0700 (PDT) Date: Thu, 16 Oct 2014 10:56:42 +0200 From: Mathieu Desnoyers Subject: Re: [PATCH v11 03/21] mm: Fix XIP fault vs truncate race Message-ID: <20141016085642.GB19075@thinkos.etherlink> References: <1411677218-29146-1-git-send-email-matthew.r.wilcox@intel.com> <1411677218-29146-4-git-send-email-matthew.r.wilcox@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1411677218-29146-4-git-send-email-matthew.r.wilcox@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 25-Sep-2014 04:33:20 PM, Matthew Wilcox wrote: > Pagecache faults recheck i_size after taking the page lock to ensure that > the fault didn't race against a truncate. We don't have a page to lock > in the XIP case, so use the i_mmap_mutex instead. It is locked in the > truncate path in unmap_mapping_range() after updating i_size. So while > we hold it in the fault path, we are guaranteed that either i_size has > already been updated in the truncate path, or that the truncate will > subsequently call zap_page_range_single() and so remove the mapping we > have just inserted. > > There is a window of time in which i_size has been reduced and the > thread has a mapping to a page which will be removed from the file, > but this is harmless as the page will not be allocated to a different > purpose before the thread's access to it is revoked. > > Signed-off-by: Matthew Wilcox > Reviewed-by: Jan Kara > Acked-by: Kirill A. Shutemov Reviewed-by: Mathieu Desnoyers > --- > mm/filemap_xip.c | 24 ++++++++++++++++++++++-- > 1 file changed, 22 insertions(+), 2 deletions(-) > > diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c > index d8d9fe3..c8d23e9 100644 > --- a/mm/filemap_xip.c > +++ b/mm/filemap_xip.c > @@ -260,8 +260,17 @@ again: > __xip_unmap(mapping, vmf->pgoff); > > found: > + /* We must recheck i_size under i_mmap_mutex */ > + mutex_lock(&mapping->i_mmap_mutex); > + size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> > + PAGE_CACHE_SHIFT; > + if (unlikely(vmf->pgoff >= size)) { > + mutex_unlock(&mapping->i_mmap_mutex); > + return VM_FAULT_SIGBUS; > + } > err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address, > xip_pfn); > + mutex_unlock(&mapping->i_mmap_mutex); > if (err == -ENOMEM) > return VM_FAULT_OOM; > /* > @@ -285,16 +294,27 @@ found: > } > if (error != -ENODATA) > goto out; > + > + /* We must recheck i_size under i_mmap_mutex */ > + mutex_lock(&mapping->i_mmap_mutex); > + size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> > + PAGE_CACHE_SHIFT; > + if (unlikely(vmf->pgoff >= size)) { > + ret = VM_FAULT_SIGBUS; > + goto unlock; > + } > /* not shared and writable, use xip_sparse_page() */ > page = xip_sparse_page(); > if (!page) > - goto out; > + goto unlock; > err = vm_insert_page(vma, (unsigned long)vmf->virtual_address, > page); > if (err == -ENOMEM) > - goto out; > + goto unlock; > > ret = VM_FAULT_NOPAGE; > +unlock: > + mutex_unlock(&mapping->i_mmap_mutex); > out: > write_seqcount_end(&xip_sparse_seq); > mutex_unlock(&xip_sparse_mutex); > -- > 2.1.0 > > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com Key fingerprint: 2A0B 4ED9 15F2 D3FA 45F5 B162 1728 0A97 8118 6ACF -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org