From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: [PATCH] sg direct io/mmap oops Date: Tue, 30 Aug 2005 21:14:21 +1000 Message-ID: <43143F8D.3080904@torque.net> Reply-To: dougg@torque.net Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------080302010103080906090004" Return-path: Received: from zorg.st.net.au ([203.16.233.9]:31649 "EHLO borg.st.net.au") by vger.kernel.org with ESMTP id S1751372AbVH3LON (ORCPT ); Tue, 30 Aug 2005 07:14:13 -0400 Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org Cc: ahmed.teirelbar@adic.com, Kai.Makisara@kolumbus.fi, James.Bottomley@SteelEye.com This is a multi-part message in MIME format. --------------080302010103080906090004 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Back in the lk 2.4 series it was possible with the sgm_dd utility to do a zero copy transfer between two disks (or 2 locations on the same disk). That was done by doing mmap-ed IO on the read and direct IO on the write with the sg driver. Well that no longer works in the lk 2.6 series because the sg (and st) driver uses get_user_pages() for direct IO and that returns -EFAULT when VM_IO is set on any of the user pages it is trying use. Pages that are mmap-ed have VM_IO set. I can live with that: dio and mmap-ed IO work separately and dio can work on both sides of a transfer. This was brought to my attention by Ahmed Teirelbar with lk 2.6.5 . Worse, when tested in lk 2.6.12 and lk 2.6.13, attempting dio/mmap caused the sg driver to oops (due to empty entries in a scatter gather list). Ahmed proposed the following patch which both of us have tested. I have alerted Kai M. as the same fix is needed in the st driver IMO. Changelog: - check error return (a negative integer) properly after the get_user_pages() call that sets up direct IO Signed-off-by: Douglas Gilbert Doug Gilbert --------------080302010103080906090004 Content-Type: text/x-patch; name="sg_2613mm.diff" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="sg_2613mm.diff" --- linux/drivers/scsi/sg.c 2005-08-29 18:28:23.000000000 +1000 +++ linux/drivers/scsi/sg.c2613mm 2005-08-30 15:09:04.000000000 +1000 @@ -61,7 +61,7 @@ #ifdef CONFIG_SCSI_PROC_FS #include -static char *sg_version_date = "20050328"; +static char *sg_version_date = "20050830"; static int sg_proc_init(void); static void sg_proc_cleanup(void); @@ -1831,7 +1831,8 @@ up_read(¤t->mm->mmap_sem); /* Errors and no page mapped should return here */ - if (res < nr_pages) + /* Beware of signed to unsigned integer promotions!! */ + if ((res < 0) || (res < nr_pages)) goto out_unmap; for (i=0; i < nr_pages; i++) { --------------080302010103080906090004--