[PATCH #upstream-fixes] libata: be less of a drama queen on empty data commands

[Tejun Heo <tj@kernel.org>]

ata_qc_issue() BUG_ON()s on data commands w/o data, which may be
submitted via SG_IO.  Be less of a drama queen and just trigger
WARN_ON_ONCE() and fail the command with AC_ERR_SYSTEM.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Stefan Hübner <stefan.huebner@stud.tu-ilmenau.de>
---
 drivers/ata/libata-core.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 7ef7c4f..c035b3d 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -5111,15 +5111,18 @@ void ata_qc_issue(struct ata_queued_cmd *qc)
 	qc->flags |= ATA_QCFLAG_ACTIVE;
 	ap->qc_active |= 1 << qc->tag;

-	/* We guarantee to LLDs that they will have at least one
+	/*
+	 * We guarantee to LLDs that they will have at least one
 	 * non-zero sg if the command is a data command.
 	 */
-	BUG_ON(ata_is_data(prot) && (!qc->sg || !qc->n_elem || !qc->nbytes));
+	if (WARN_ON_ONCE(ata_is_data(prot) &&
+			 (!qc->sg || !qc->n_elem || !qc->nbytes)))
+		goto sys_err;

 	if (ata_is_dma(prot) || (ata_is_pio(prot) &&
 				 (ap->flags & ATA_FLAG_PIO_DMA)))
 		if (ata_sg_setup(qc))
-			goto sg_err;
+			goto sys_err;

 	/* if device is sleeping, schedule reset and abort the link */
 	if (unlikely(qc->dev->flags & ATA_DFLAG_SLEEPING)) {
@@ -5136,7 +5139,7 @@ void ata_qc_issue(struct ata_queued_cmd *qc)
 		goto err;
 	return;

-sg_err:
+sys_err:
 	qc->err_mask |= AC_ERR_SYSTEM;
 err:
 	ata_qc_complete(qc);