xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

atari_scsi: Fix atari_scsi deadlocks on Falcon

Browse Source 
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>
This commit is contained in:
Finn Thain
2014-11-12 16:12:08 +11:00
committed by Christoph Hellwig
parent cbad48deb3
commit 16b29e75a7
4 changed files with 66 additions and 107 deletions
Download Patch File Download Diff File Expand all files Collapse all files

75
drivers/scsi/atari_scsi.c
View File

@@ -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;
}