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authorFinn Thain <fthain@telegraphics.com.au>2014-11-12 08:12:08 +0300
committerChristoph Hellwig <hch@lst.de>2014-11-20 11:11:13 +0300
commit16b29e75a78ae03250233468b68f7ae467d3dc7a (patch)
treea5ba9e016d5557d2a6f5fb60dc83ae906ae771af /drivers/scsi/atari_scsi.c
parentcbad48deb38d8e442db9760ca1f950cd24429707 (diff)
downloadlinux-16b29e75a78ae03250233468b68f7ae467d3dc7a.tar.xz
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>
Diffstat (limited to 'drivers/scsi/atari_scsi.c')
-rw-r--r--drivers/scsi/atari_scsi.c75
1 files changed, 14 insertions, 61 deletions
diff --git a/drivers/scsi/atari_scsi.c b/drivers/scsi/atari_scsi.c
index 48fabebdbbb0..b2e86d0630ce 100644
--- a/drivers/scsi/atari_scsi.c
+++ b/drivers/scsi/atari_scsi.c
@@ -184,7 +184,7 @@ static void atari_scsi_fetch_restbytes(void);
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
@@ -473,17 +473,10 @@ static void atari_scsi_fetch_restbytes(void)
#endif /* REAL_DMA */
-static int falcon_got_lock = 0;
-static DECLARE_WAIT_QUEUE_HEAD(falcon_fairness_wait);
-static int falcon_trying_lock = 0;
-static DECLARE_WAIT_QUEUE_HEAD(falcon_try_wait);
static int falcon_dont_release = 0;
/* This function releases the lock on the DMA chip if there is no
- * connected command and the disconnected queue is empty. On
- * releasing, instances of falcon_get_lock are awoken, that put
- * themselves to sleep for fairness. They can now try to get the lock
- * again (but others waiting longer more probably will win).
+ * connected command and the disconnected queue is empty.
*/
static void falcon_release_lock_if_possible(struct NCR5380_hostdata *hostdata)
@@ -495,20 +488,12 @@ static void falcon_release_lock_if_possible(struct NCR5380_hostdata *hostdata)
local_irq_save(flags);
- if (falcon_got_lock && !hostdata->disconnected_queue &&
- !hostdata->issue_queue && !hostdata->connected) {
-
- if (falcon_dont_release) {
-#if 0
- printk("WARNING: Lock release not allowed. Ignored\n");
-#endif
- local_irq_restore(flags);
- return;
- }
- falcon_got_lock = 0;
+ if (!hostdata->disconnected_queue &&
+ !hostdata->issue_queue &&
+ !hostdata->connected &&
+ !falcon_dont_release &&
+ stdma_is_locked_by(scsi_falcon_intr))
stdma_release();
- wake_up(&falcon_fairness_wait);
- }
local_irq_restore(flags);
}
@@ -517,51 +502,19 @@ static void falcon_release_lock_if_possible(struct NCR5380_hostdata *hostdata)
* If the DMA isn't locked already for SCSI, it tries to lock it by
* calling stdma_lock(). But if the DMA is locked by the SCSI code and
* there are other drivers waiting for the chip, we do not issue the
- * command immediately but wait on 'falcon_fairness_queue'. We will be
- * waked up when the DMA is unlocked by some SCSI interrupt. After that
- * we try to get the lock again.
- * But we must be prepared that more than one instance of
- * falcon_get_lock() is waiting on the fairness queue. They should not
- * try all at once to call stdma_lock(), one is enough! For that, the
- * first one sets 'falcon_trying_lock', others that see that variable
- * set wait on the queue 'falcon_try_wait'.
- * Complicated, complicated.... Sigh...
+ * command immediately but tell the SCSI mid-layer to defer.
*/
-static void falcon_get_lock(void)
+static int falcon_get_lock(void)
{
- unsigned long flags;
-
if (IS_A_TT())
- return;
+ return 1;
- local_irq_save(flags);
+ if (in_interrupt())
+ return stdma_try_lock(scsi_falcon_intr, NULL);
- wait_event_cmd(falcon_fairness_wait,
- 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");
- if (!falcon_trying_lock) {
- falcon_trying_lock = 1;
- stdma_lock(scsi_falcon_intr, NULL);
- falcon_got_lock = 1;
- falcon_trying_lock = 0;
- wake_up(&falcon_try_wait);
- } else {
- wait_event_cmd(falcon_try_wait,
- falcon_got_lock && !falcon_trying_lock,
- local_irq_restore(flags),
- local_irq_save(flags));
- }
- }
-
- local_irq_restore(flags);
- if (!falcon_got_lock)
- panic("Falcon SCSI: someone stole the lock :-(\n");
+ stdma_lock(scsi_falcon_intr, NULL);
+ return 1;
}