From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Jenkins Subject: scsi: Generalise last_sector_bug; fixes regression and potential future issues on USB cardreaders Date: Thu, 24 Jul 2008 11:15:55 +0100 Message-ID: <4888565B.4020102@tuffmail.co.uk> References: <4888524D.9070906@tuffmail.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from ik-out-1112.google.com ([66.249.90.181]:41201 "EHLO ik-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751712AbYGXKPh (ORCPT ); Thu, 24 Jul 2008 06:15:37 -0400 Received: by ik-out-1112.google.com with SMTP id c28so2089088ika.5 for ; Thu, 24 Jul 2008 03:15:35 -0700 (PDT) In-Reply-To: <4888524D.9070906@tuffmail.co.uk> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James.Bottomley@HansenPartnership.com Cc: linux-scsi@vger.kernel.org, Alan Stern The last_sector_bug flag was added to work around a bug in certain usb cardreaders, where they would crash if a multiple sector read included the last sector. The original implementation avoids this by e.g. splitting an 8 sector read which includes the last sector into a 7 sector read, and a single sector read for the last sector. The flag is enabled for all USB devices. This revealed a second bug in other usb cardreaders, which crash when they get a multiple sector read which stops 1 sector short of the last sector. Affected hardware includes the Kingston "MobileLite" external USB cardreader and the internal USB cardreader on the Asus EeePC. Extend the last_sector_bug workaround to ensure that any access which touches the last 8 hardware sectors of the device is a single sector long. Requests are shrunk as necessary to meet this constraint. This gives us a safety margin against potential unknown or future bugs affecting multi-sector access to the end of the device. The two known bugs only affect the last 2 sectors. However, they suggest that these devices are prone to fencepost errors and that multi-sector access to the end of the device is not well tested. Popular OS's use multi-sector accesses, but they rarely read the last few sectors. Linux (with udev & vol_id) automatically reads sectors from the end of the device on insertion. It is assumed that single sector accesses are more thoroughly tested during development. Signed-off-by: Alan Jenkins Tested-by: Alan Jenkins diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index 01cefbb..2415a1b 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -406,13 +406,23 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq) } /* - * Some devices (some sdcards for one) don't like it if the - * last sector gets read in a larger then 1 sector read. + * Some sd cardreaders can't handle multisector accesses which touch + * the last one or two hardware sectors. There are likely to be even + * buggier devices, so apply a workaround to the last eight sectors. */ - if (unlikely(sdp->last_sector_bug && - rq->nr_sectors > sdp->sector_size / 512 && - block + this_count == get_capacity(disk))) - this_count -= sdp->sector_size / 512; + if (sdp->last_sector_bug) { + unsigned threshold = get_capacity(disk) - 8 * (sdp->sector_size / 512); + + if (block + this_count <= threshold) { + ; /* Okay as is */ + } else if (block < threshold) { + /* Access up to the threshold but not beyond */ + this_count = threshold - block; + } else { + /* Access only a single hardware sector */ + this_count = sdp->sector_size / 512; + } + } SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt, "block=%llu\n", (unsigned long long)block)); diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h index f6a9fe0..0d8d9c1 100644 --- a/include/scsi/scsi_device.h +++ b/include/scsi/scsi_device.h @@ -139,7 +139,8 @@ struct scsi_device { unsigned fix_capacity:1; /* READ_CAPACITY is too high by 1 */ unsigned guess_capacity:1; /* READ_CAPACITY might be too high by 1 */ unsigned retry_hwerror:1; /* Retry HARDWARE_ERROR */ - unsigned last_sector_bug:1; /* Always read last sector in a 1 sector read */ + unsigned last_sector_bug:1; /* do not use multisector accesses on + the last 8 hardware sectors */ DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */ struct list_head event_list; /* asserted events */