atari_scsi: Fix atari_scsi deadlocks on Falcon
Don't disable irqs when waiting for the ST DMA "lock"; its release may
require an interrupt.
Introduce stdma_try_lock() for use in soft irq context. atari_scsi now tells
the SCSI mid-layer to defer queueing a command if the ST DMA lock is not
available, as per Michael's patch:
http://marc.info/?l=linux-m68k&m=139095335824863&w=2
The falcon_got_lock variable is race prone: we can't disable IRQs while
waiting to acquire the lock, so after acquiring it there must be some
interval during which falcon_got_lock remains false. Introduce
stdma_is_locked_by() to replace falcon_got_lock.
The falcon_got_lock tests in the EH handlers are incorrect these days. It
can happen that an EH handler is called after a command completes normally.
Remove these checks along with falcon_got_lock.
Also remove the complicated and racy fairness wait queues. If fairness is an
issue (when SCSI competes with IDE for the ST DMA interrupt), the solution
is likely to be a lower value for host->can_queue.
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/arch/m68k/atari/stdma.c b/arch/m68k/atari/stdma.c
index ddbf43c..e5a6659 100644
--- a/arch/m68k/atari/stdma.c
+++ b/arch/m68k/atari/stdma.c
@@ -59,6 +59,31 @@
/************************* End of Prototypes **************************/
+/**
+ * stdma_try_lock - attempt to acquire ST DMA interrupt "lock"
+ * @handler: interrupt handler to use after acquisition
+ *
+ * Returns !0 if lock was acquired; otherwise 0.
+ */
+
+int stdma_try_lock(irq_handler_t handler, void *data)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ if (stdma_locked) {
+ local_irq_restore(flags);
+ return 0;
+ }
+
+ stdma_locked = 1;
+ stdma_isr = handler;
+ stdma_isr_data = data;
+ local_irq_restore(flags);
+ return 1;
+}
+EXPORT_SYMBOL(stdma_try_lock);
+
/*
* Function: void stdma_lock( isrfunc isr, void *data )
@@ -78,19 +103,10 @@
void stdma_lock(irq_handler_t handler, void *data)
{
- unsigned long flags;
-
- local_irq_save(flags); /* protect lock */
-
/* Since the DMA is used for file system purposes, we
have to sleep uninterruptible (there may be locked
buffers) */
- wait_event(stdma_wait, !stdma_locked);
-
- stdma_locked = 1;
- stdma_isr = handler;
- stdma_isr_data = data;
- local_irq_restore(flags);
+ wait_event(stdma_wait, stdma_try_lock(handler, data));
}
EXPORT_SYMBOL(stdma_lock);
@@ -122,22 +138,25 @@
EXPORT_SYMBOL(stdma_release);
-/*
- * Function: int stdma_others_waiting( void )
+/**
+ * stdma_is_locked_by - allow lock holder to check whether it needs to release.
+ * @handler: interrupt handler previously used to acquire lock.
*
- * Purpose: Check if someone waits for the ST-DMA lock.
- *
- * Inputs: none
- *
- * Returns: 0 if no one is waiting, != 0 otherwise
- *
+ * Returns !0 if locked for the given handler; 0 otherwise.
*/
-int stdma_others_waiting(void)
+int stdma_is_locked_by(irq_handler_t handler)
{
- return waitqueue_active(&stdma_wait);
+ unsigned long flags;
+ int result;
+
+ local_irq_save(flags);
+ result = stdma_locked && (stdma_isr == handler);
+ local_irq_restore(flags);
+
+ return result;
}
-EXPORT_SYMBOL(stdma_others_waiting);
+EXPORT_SYMBOL(stdma_is_locked_by);
/*