From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d12nrmr1607.megacenter.de.ibm.com (d12nrmr1607.megacenter.de.ibm.com [9.149.167.49]) by mtagate4.de.ibm.com (8.13.8/8.13.8) with ESMTP id l1QI4AP7127770 for ; Mon, 26 Feb 2007 18:04:10 GMT Received: from d12av02.megacenter.de.ibm.com (d12av02.megacenter.de.ibm.com [9.149.165.228]) by d12nrmr1607.megacenter.de.ibm.com (8.13.8/8.13.8/NCO v8.2) with ESMTP id l1QI4Av72129978 for ; Mon, 26 Feb 2007 19:04:10 +0100 Received: from d12av02.megacenter.de.ibm.com (loopback [127.0.0.1]) by d12av02.megacenter.de.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id l1QI4AGp030997 for ; Mon, 26 Feb 2007 19:04:10 +0100 Subject: [RFC] [patch] mm: fix xip issue with /dev/zero From: Carsten Otte In-Reply-To: References: <1171628558.7328.16.camel@cotte.boeblingen.de.ibm.com> Content-Type: text/plain Date: Mon, 26 Feb 2007 19:04:10 +0100 Message-Id: <1172513050.5685.21.camel@cotte.boeblingen.de.ibm.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Hugh Dickins Cc: Nick Piggin , Linux Memory Management List-ID: Thanks for your review feedback Hugh, I do appreciate it. Here comes my second attempt: This patch fixes the bug, that reading into xip mapping from /dev/zero fills the user page table with ZERO_PAGE() entries. Later on, xip cannot tell which pages have been ZERO_PAGE() filled by access to a sparse mapping, and which ones origin from /dev/zero. It will unmap ZERO_PAGE from all mappings when filling the sparse hole with data. xip does now use its own zeroed page for its sparse mappings. Signed-off-by: Carsten Otte --- diff -pruN linux-2.6/mm/filemap_xip.c linux-2.6+fix/mm/filemap_xip.c --- linux-2.6/mm/filemap_xip.c 2007-02-26 13:46:28.000000000 +0100 +++ linux-2.6+fix/mm/filemap_xip.c 2007-02-26 18:45:15.000000000 +0100 @@ -17,6 +17,31 @@ #include "filemap.h" /* + * We do use our own empty page to avoid interference with other users + * of ZERO_PAGE(), such as /dev/zero + */ +static struct page *__xip_sparse_page = NULL; +static DEFINE_SPINLOCK(xip_alloc_lock); + +static struct page *xip_sparse_page(void) +{ + unsigned long tmp; + + if (!__xip_sparse_page) { + tmp = get_zeroed_page(GFP_ATOMIC); + if (!tmp) + return NULL; + spin_lock(&xip_alloc_lock); + if (!__xip_sparse_page) + __xip_sparse_page = virt_to_page(tmp); + else + free_page (tmp); + spin_unlock(&xip_alloc_lock); + } + return __xip_sparse_page; +} + +/* * This is a file read routine for execute in place files, and uses * the mapping->a_ops->get_xip_page() function for the actual low-level * stuff. @@ -63,12 +88,18 @@ do_xip_mapping_read(struct address_space page = mapping->a_ops->get_xip_page(mapping, index*(PAGE_SIZE/512), 0); - if (!page) + if (!page) { + desc->error = -EIO; goto no_xip_page; + } if (unlikely(IS_ERR(page))) { if (PTR_ERR(page) == -ENODATA) { /* sparse */ - page = ZERO_PAGE(0); + page = xip_sparse_page(); + if (!page) { + desc->error = -ENOMEM; + goto no_xip_page; + } } else { desc->error = PTR_ERR(page); goto out; @@ -102,7 +133,6 @@ do_xip_mapping_read(struct address_space no_xip_page: /* Did not get the page. Report it */ - desc->error = -EIO; goto out; } @@ -162,7 +192,7 @@ EXPORT_SYMBOL_GPL(xip_file_sendfile); * xip_write * * This function walks all vmas of the address_space and unmaps the - * ZERO_PAGE when found at pgoff. Should it go in rmap.c? + * xip_sparse_page() when found at pgoff. */ static void __xip_unmap (struct address_space * mapping, @@ -183,7 +213,11 @@ __xip_unmap (struct address_space * mapp address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); BUG_ON(address < vma->vm_start || address >= vma->vm_end); - page = ZERO_PAGE(0); + page = xip_sparse_page(); + if (!page) + /* cannot allocate xip page, is not mapped anywhere */ + goto out_unlock; + pte = page_check_address(page, mm, address, &ptl); if (pte) { /* Nuke the page table entry. */ @@ -196,6 +230,7 @@ __xip_unmap (struct address_space * mapp page_cache_release(page); } } +out_unlock: spin_unlock(&mapping->i_mmap_lock); } @@ -245,12 +280,13 @@ xip_file_nopage(struct vm_area_struct * /* unmap page at pgoff from all other vmas */ __xip_unmap(mapping, pgoff); } else { - /* not shared and writable, use ZERO_PAGE() */ - page = ZERO_PAGE(0); + /* not shared and writable, use xip_sparse_page() */ + page = xip_sparse_page(); } out: - page_cache_get(page); + if (page) + page_cache_get(page); return page; } -- 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