From 16b29e75a78ae03250233468b68f7ae467d3dc7a Mon Sep 17 00:00:00 2001 From: Finn Thain Date: Wed, 12 Nov 2014 16:12:08 +1100 Subject: 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 Reviewed-by: Hannes Reinecke Tested-by: Michael Schmitz Acked-by: Geert Uytterhoeven Signed-off-by: Christoph Hellwig --- arch/m68k/atari/stdma.c | 61 ++++++++++++++++++++++++++++++++----------------- 1 file changed, 40 insertions(+), 21 deletions(-) (limited to 'arch/m68k/atari') diff --git a/arch/m68k/atari/stdma.c b/arch/m68k/atari/stdma.c index ddbf43ca8858..e5a66596b116 100644 --- a/arch/m68k/atari/stdma.c +++ b/arch/m68k/atari/stdma.c @@ -59,6 +59,31 @@ static irqreturn_t stdma_int (int irq, void *dummy); /************************* 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 @@ static irqreturn_t stdma_int (int irq, void *dummy); 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 @@ void stdma_release(void) EXPORT_SYMBOL(stdma_release); -/* - * Function: int stdma_others_waiting( void ) - * - * Purpose: Check if someone waits for the ST-DMA lock. - * - * Inputs: none - * - * Returns: 0 if no one is waiting, != 0 otherwise +/** + * stdma_is_locked_by - allow lock holder to check whether it needs to release. + * @handler: interrupt handler previously used to acquire lock. * + * 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); /* -- cgit v1.2.3