diff options
author | Alan Jenkins <alan-jenkins@tuffmail.co.uk> | 2008-07-27 12:38:42 +0400 |
---|---|---|
committer | James Bottomley <James.Bottomley@HansenPartnership.com> | 2008-07-27 18:16:13 +0400 |
commit | 2b142900784c6e38c8d39fa57d5f95ef08e735d8 (patch) | |
tree | e7d51b58df76e864c91ff7ffca0229027328c588 /drivers | |
parent | 4cfc51017db3e3f4eaaa2cb436a905097a4f08e2 (diff) | |
download | linux-2b142900784c6e38c8d39fa57d5f95ef08e735d8.tar.xz |
[SCSI] extend the last_sector_bug flag to cover more sectors
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 <alan-jenkins@tuffmail.co.uk>
Tested-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/scsi/sd.c | 21 | ||||
-rw-r--r-- | drivers/scsi/sd.h | 6 |
2 files changed, 21 insertions, 6 deletions
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index 8e08d51a0f05..e5e7d7856454 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -375,6 +375,7 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq) struct gendisk *disk = rq->rq_disk; struct scsi_disk *sdkp; sector_t block = rq->sector; + sector_t threshold; unsigned int this_count = rq->nr_sectors; unsigned int timeout = sdp->timeout; int ret; @@ -422,13 +423,21 @@ 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 card readers can't handle multi-sector accesses which touch + * the last one or two hardware sectors. Split accesses as needed. */ - 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; + threshold = get_capacity(disk) - SD_LAST_BUGGY_SECTORS * + (sdp->sector_size / 512); + + if (unlikely(sdp->last_sector_bug && block + this_count > threshold)) { + 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/drivers/scsi/sd.h b/drivers/scsi/sd.h index 550b2f70a1f8..95b9f06534d5 100644 --- a/drivers/scsi/sd.h +++ b/drivers/scsi/sd.h @@ -31,6 +31,12 @@ */ #define SD_BUF_SIZE 512 +/* + * Number of sectors at the end of the device to avoid multi-sector + * accesses to in the case of last_sector_bug + */ +#define SD_LAST_BUGGY_SECTORS 8 + struct scsi_disk { struct scsi_driver *driver; /* always &sd_template */ struct scsi_device *device; |