ncr5380: Fix soft lockups

Because of the rudimentary design of the chip, it is necessary to poll the
SCSI bus signals during PIO and this tends to hog the CPU. The driver will
accept new commands while others execute, and this causes a soft lockup
because the workqueue item will not terminate until the issue queue is
emptied.

When exercising dmx3191d using sequential IO from dd, the driver is sent
512 KiB WRITE commands and 128 KiB READs. For a PIO transfer, the rate is
is only about 300 KiB/s, so these are long-running commands. And although
PDMA may run at several MiB/s, interrupts are disabled for the duration
of the transfer.

Fix the unresponsiveness and soft lockup issues by calling cond_resched()
after each command is completed and by limiting max_sectors for drivers
that don't implement real DMA.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Ondrej Zary <linux@rainbow-software.org>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/scsi/NCR5380.c b/drivers/scsi/NCR5380.c
index 9616f397e134..38b03af36a6a 100644
--- a/drivers/scsi/NCR5380.c
+++ b/drivers/scsi/NCR5380.c
@@ -890,10 +890,10 @@ static void NCR5380_main(struct work_struct *work)
         struct scsi_cmnd *cmd;
         int done;
         
-        spin_lock_irq(&hostdata->lock);
         do {
                 done = 1;
 
+                spin_lock_irq(&hostdata->lock);
                 while (!hostdata->connected &&
                        (cmd = dequeue_next_cmd(instance))) {
 
@@ -930,8 +930,10 @@ static void NCR5380_main(struct work_struct *work)
                         NCR5380_information_transfer(instance);
                         done = 0;
                 }
+                spin_unlock_irq(&hostdata->lock);
+                if (!done)
+                        cond_resched();
         } while (!done);
-        spin_unlock_irq(&hostdata->lock);
 }
 
 #ifndef DONT_USE_INTR