Commit 4d2de3a5 authored by Tony Battersby's avatar Tony Battersby Committed by James Bottomley
Browse files

[SCSI] fix BUG when sum(scatterlist) > bufflen

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

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: default avatarTony Battersby <>
Acked-by: default avatarMike Christie <>
Signed-off-by: default avatarJames Bottomley <>
parent 76d78300
......@@ -301,7 +301,6 @@ 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) {
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