From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755483AbaA1VBd (ORCPT ); Tue, 28 Jan 2014 16:01:33 -0500 Received: from mta-out.inet.fi ([195.156.147.13]:33948 "EHLO jenni1.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755043AbaA1VBc (ORCPT ); Tue, 28 Jan 2014 16:01:32 -0500 Date: Tue, 28 Jan 2014 23:01:26 +0200 From: "Kirill A. Shutemov" To: Andrew Morton Cc: Mark Rutland , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: readahead: fix do_readahead for no readpage(s) Message-ID: <20140128210126.GA27556@node.dhcp.inet.fi> References: <1390907659-11675-1-git-send-email-mark.rutland@arm.com> <20140128120301.581c90caeb1c49e346b6aa66@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140128120301.581c90caeb1c49e346b6aa66@linux-foundation.org> User-Agent: Mutt/1.5.22.1-rc1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 28, 2014 at 12:03:01PM -0800, Andrew Morton wrote: > On Tue, 28 Jan 2014 11:14:19 +0000 Mark Rutland wrote: > > > Commit 63d0f0a3c7e1 (mm/readahead.c:do_readhead(): don't check for > > ->readpage) unintentionally made do_readahead return 0 for all valid > > files regardless of whether readahead was supported, rather than the > > expected -EINVAL. This gets forwarded on to userspace, and results in > > sys_readahead appearing to succeed in cases that don't make sense (e.g. > > when called on pipes or sockets). This issue is detected by the LTP > > readahead01 testcase. > > How can this be? > > : static ssize_t > : do_readahead(struct address_space *mapping, struct file *filp, > : pgoff_t index, unsigned long nr) > : { > : if (!mapping || !mapping->a_ops) > : return -EINVAL; > : > : return force_page_cache_readahead(mapping, filp, index, nr); It's not what we have in Linus' tree. force_page_cache_readahead() return code is unused: force_page_cache_readahead(mapping, filp, index, nr); return 0; > : } > > and > > : int force_page_cache_readahead(struct address_space *mapping, struct file *filp, > : pgoff_t offset, unsigned long nr_to_read) > : { > : if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) > : return -EINVAL; > > Clearly, do_readahead() will return -EINVAL if neither ->readpage or > ->readpages are implemented. > > I can see that the behaviour would change if the address_space > implements only one of ->readpage and ->readpages, but that doesn't > appear to match your description and the new behaviour is correct - we > can now perform readahead for address_spaces which implement > ->readpages and not ->readpage (which would be odd and might not work > for other reasons..). > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Kirill A. Shutemov