SCSI: add 1024 max sectors black list flag

This works around a issue with qnap iscsi targets not handling large IOs
very well.

The target returns:

VPD INQUIRY: Block limits page (SBC)
  Maximum compare and write length: 1 blocks
  Optimal transfer length granularity: 1 blocks
  Maximum transfer length: 4294967295 blocks
  Optimal transfer length: 4294967295 blocks
  Maximum prefetch, xdread, xdwrite transfer length: 0 blocks
  Maximum unmap LBA count: 8388607
  Maximum unmap block descriptor count: 1
  Optimal unmap granularity: 16383
  Unmap granularity alignment valid: 0
  Unmap granularity alignment: 0
  Maximum write same length: 0xffffffff blocks
  Maximum atomic transfer length: 0
  Atomic alignment: 0
  Atomic transfer length granularity: 0

and it is *sometimes* able to handle at least one IO of size up to 8 MB. We
have seen in traces where it will sometimes work, but other times it
looks like it fails and it looks like it returns failures if we send
multiple large IOs sometimes. Also it looks like it can return 2 different
errors. It will sometimes send iscsi reject errors indicating out of
resources or it will send invalid cdb illegal requests check conditions.
And then when it sends iscsi rejects it does not seem to handle retries
when there are command sequence holes, so I could not just add code to
try and gracefully handle that error code.

The problem is that we do not have a good contact for the company,
so we are not able to determine under what conditions it returns
which error and why it sometimes works.

So, this patch just adds a new black list flag to set targets like this to
the old max safe sectors of 1024. The max_hw_sectors changes added in 3.19
caused this regression, so I also ccing stable.

Reported-by: Christian Hesse <list@eworm.de>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Cc: stable@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 60aae01caa89..6efab1c455e1 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -897,6 +897,12 @@ static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
 	 */
 	if (*bflags & BLIST_MAX_512)
 		blk_queue_max_hw_sectors(sdev->request_queue, 512);
+	/*
+	 * Max 1024 sector transfer length for targets that report incorrect
+	 * max/optimal lengths and relied on the old block layer safe default
+	 */
+	else if (*bflags & BLIST_MAX_1024)
+		blk_queue_max_hw_sectors(sdev->request_queue, 1024);
 
 	/*
 	 * Some devices may not want to have a start command automatically