SCSI: fix BUG when sum(scatterlist) > bufflen

commit: 4d2de3a50ce19af2008a90636436a1bf5b3b697b

When sending a SCSI command to a tape drive via the SCSI Generic (sg)
driver, if the command has a data transfer length more than
scatter_elem_sz (32 KB default) and not a multiple of 512, then I either
hit BUG_ON(!valid_dma_direction(direction)) in dma_unmap_sg() or else
the command never completes (depending on the LLDD).

When constructing scatterlists, the sg driver rounds up the scatterlist
element sizes to be a multiple of 512.  This can result in
sum(scatterlist lengths) > bufflen.  In this case, scsi_req_map_sg()
incorrectly sets bio->bi_size to sum(scatterlist lengths) rather than to
bufflen.  When the command completes, req_bio_endio() detects that
bio->bi_size != 0, and so it doesn't call bio_endio().  This causes the
command to be resubmitted, resulting in BUG_ON or the command never
completing.

This patch makes scsi_req_map_sg() set bio->bi_size to bufflen rather
than to sum(scatterlist lengths), which fixes the problem.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index a9ac5b1b1667f339d5db22760e308b18ac9a3a71..273728e1c9de5bf03cee5053e073ca8023a6d61e 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -298,7 +298,6 @@ static int scsi_req_map_sg(struct request *rq, struct scatterlist *sgl,
                page = sg_page(sg);
                off = sg->offset;
                len = sg->length;
-               data_len += len;
 
                while (len > 0 && data_len > 0) {
                        /*