[PATCH 3/3] m68k/atari - atari_scsi lock fixes: punt if deadlocked

Michael Schmitz
2014-01-28T23:55:24Z

In case a SCSI command is queued from softirq context, and another
driver currently holds the ST-DMA lock, tell the SCSI midlevel to
hold off queueing commands for now. Something will hopefully resume
play later.

Signed-off-by: Michael Schmitz <schmitz@debian.org>
---
drivers/scsi/atari_NCR5380.c | 12 +++++++++---
drivers/scsi/atari_scsi.c | 26 +++++++++++++++++++++-----
2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/atari_NCR5380.c b/drivers/scsi/atari_NCR5380.c
index 465e63d..90a90e8 100644
--- a/drivers/scsi/atari_NCR5380.c
+++ b/drivers/scsi/atari_NCR5380.c
@@ -967,9 +967,15 @@ static int NCR5380_queue_command_lck(Scsi_Cmnd *cmd, void (*done)(Scsi_Cmnd *))
* alter queues and touch the lock.
*/
if (!IS_A_TT()) {
- /* perhaps stop command timer here */
- falcon_get_lock();
- /* perhaps restart command timer here */
+ /* MSch 20140119: check whether obtaining the ST-DMA lock did
+ * succeed.
+ * If the lock could not be acquired without risking to
+ * deadlock, i.e. from softirq context with ST-DMA currently
+ * otherwise locked, defer queueing further commands.
+ */
+ if (falcon_get_lock()) {
+ return SCSI_MLQUEUE_HOST_BUSY;
+ }
}
if (!(hostdata->issue_queue) || (cmd->cmnd[0] == REQUEST_SENSE)) {
LIST(cmd, hostdata->issue_queue);
diff --git a/drivers/scsi/atari_scsi.c b/drivers/scsi/atari_scsi.c
index 5e19509..2b62ce2 100644
--- a/drivers/scsi/atari_scsi.c
+++ b/drivers/scsi/atari_scsi.c
@@ -197,7 +197,7 @@ static unsigned long atari_dma_xfer_len(unsigned long wanted_len,
static irqreturn_t scsi_tt_intr(int irq, void *dummy);
static irqreturn_t scsi_falcon_intr(int irq, void *dummy);
static void falcon_release_lock_if_possible(struct NCR5380_hostdata *hostdata);
-static void falcon_get_lock(void);
+static int falcon_get_lock(void);
#ifdef CONFIG_ATARI_SCSI_RESET_BOOT
static void atari_scsi_reset_boot(void);
#endif
@@ -541,24 +541,39 @@ static void falcon_release_lock_if_possible(struct NCR5380_hostdata *hostdata)
* Complicated, complicated.... Sigh...
*/

-static void falcon_get_lock(void)
+static int falcon_get_lock(void)
{
unsigned long flags;

if (IS_A_TT())
- return;
+ return 0;

local_irq_save(flags);

wait_event_cmd(falcon_fairness_wait,
- in_irq() || !falcon_got_lock || !stdma_others_waiting(),
+ in_interrupt() || !falcon_got_lock || !stdma_others_waiting(),
local_irq_restore(flags),
local_irq_save(flags));

while (!falcon_got_lock) {
if (in_irq())
- panic("Falcon SCSI hasn't ST-DMA lock in interrupt");
+ panic("Falcon SCSI hasn't got ST-DMA lock in irq");
if (!falcon_trying_lock) {
+ if (in_interrupt()) {
+ if (stdma_islocked()) {
+ /* MSch 20140119: problem -
+ * cannot schedule in interrupt!
+ * Unless stdma_lock can be modified
+ * to interruptible wait, this will
+ * be needed to avoid deadlocking here!
+ * Return error to indicate command
+ * queueing would deadlock, and allow
+ * queue_command() to stall queueing.
+ */
+ local_irq_restore(flags);
+ return 1;
+ }
+ }
falcon_trying_lock = 1;
stdma_lock(scsi_falcon_intr, NULL);
falcon_got_lock = 1;
@@ -575,6 +590,7 @@ static void falcon_get_lock(void)
local_irq_restore(flags);
if (!falcon_got_lock)
panic("Falcon SCSI: someone stole the lock :-(\n");
+ return 0;
}

--
1.7.0.4