[PATCH] scsi_debug: fix in_use bitmap corruption

[PATCH] scsi_debug: fix in_use bitmap corruption

[Douglas Gilbert]

Heavy testing indicates the irqsave() spinlock around the
__set_bit() is insufficient to stop following clear_bit() calls
being rarely applied out-of-order. Also the nearby failed
kzalloc() path leading to SCSI_MLQUEUE_HOST_BUSY does not
properly undo the in_use bitmap and num_in_q, fix.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
 drivers/scsi/scsi_debug.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 843cccb38cb7..4692f5b6ad13 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -5430,7 +5430,7 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 		else
 			return SCSI_MLQUEUE_HOST_BUSY;
 	}
-	__set_bit(k, sqp->in_use_bm);
+	set_bit(k, sqp->in_use_bm);
 	atomic_inc(&devip->num_in_q);
 	sqcp = &sqp->qc_arr[k];
 	sqcp->a_cmnd = cmnd;
@@ -5439,10 +5439,13 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 	spin_unlock_irqrestore(&sqp->qc_lock, iflags);
 	if (unlikely(sdebug_every_nth && sdebug_any_injecting_opt))
 		setup_inject(sqp, sqcp);
-	if (sd_dp == NULL) {
+	if (!sd_dp) {
 		sd_dp = kzalloc(sizeof(*sd_dp), GFP_ATOMIC);
-		if (sd_dp == NULL)
+		if (!sd_dp) {
+			atomic_dec(&devip->num_in_q);
+			clear_bit(k, sqp->in_use_bm);
 			return SCSI_MLQUEUE_HOST_BUSY;
+		}
 		new_sd_dp = true;
 	} else {
 		new_sd_dp = false;
-- 
2.25.1

Re: [PATCH] scsi_debug: fix in_use bitmap corruption

[Martin K. Petersen]

On Thu, 2 Jul 2020 10:53:55 -0400, Douglas Gilbert wrote:

> Heavy testing indicates the irqsave() spinlock around the
> __set_bit() is insufficient to stop following clear_bit() calls
> being rarely applied out-of-order. Also the nearby failed
> kzalloc() path leading to SCSI_MLQUEUE_HOST_BUSY does not
> properly undo the in_use bitmap and num_in_q, fix.

Applied to 5.9/scsi-queue, thanks!

[1/1] scsi: scsi_debug: Fix in_use bitmap corruption
      https://git.kernel.org/mkp/scsi/c/74595c044cb5

-- 
Martin K. Petersen	Oracle Linux Engineering