[PATCH 1/2] dmaengine: shdma: fix locking

Guennadi Liakhovetski
2011-04-29T17:09:31Z

Close multiple theoretical races, especially the one in
.device_free_chan_resources().

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
---
drivers/dma/shdma.c | 104 +++++++++++++++++++++++++++++++++-----------------
1 files changed, 68 insertions(+), 36 deletions(-)

diff --git a/drivers/dma/shdma.c b/drivers/dma/shdma.c
index b7f27f5..d0f402b 100644
--- a/drivers/dma/shdma.c
+++ b/drivers/dma/shdma.c
@@ -48,7 +48,7 @@ enum sh_dmae_desc_status {

/*
* Used for write-side mutual exclusion for the global device list,
- * read-side synchronization by way of RCU.
+ * read-side synchronization by way of RCU, and per-controller data.
*/
static DEFINE_SPINLOCK(sh_dmae_lock);
static LIST_HEAD(sh_dmae_devices);
@@ -85,22 +85,35 @@ static void dmaor_write(struct sh_dmae_device *shdev, u16 data)
*/
static void sh_dmae_ctl_stop(struct sh_dmae_device *shdev)
{
- unsigned short dmaor = dmaor_read(shdev);
+ unsigned short dmaor;
+ unsigned long flags;
+
+ spin_lock_irqsave(&sh_dmae_lock, flags);

+ dmaor = dmaor_read(shdev);
dmaor_write(shdev, dmaor & ~(DMAOR_NMIF | DMAOR_AE | DMAOR_DME));
+
+ spin_unlock_irqrestore(&sh_dmae_lock, flags);
}

static int sh_dmae_rst(struct sh_dmae_device *shdev)
{
unsigned short dmaor;
+ unsigned long flags;

- sh_dmae_ctl_stop(shdev);
- dmaor = dmaor_read(shdev) | shdev->pdata->dmaor_init;
+ spin_lock_irqsave(&sh_dmae_lock, flags);

- dmaor_write(shdev, dmaor);
- if (dmaor_read(shdev) & (DMAOR_AE | DMAOR_NMIF)) {
- pr_warning("dma-sh: Can't initialize DMAOR.\n");
- return -EINVAL;
+ dmaor = dmaor_read(shdev) & ~(DMAOR_NMIF | DMAOR_AE | DMAOR_DME);
+
+ dmaor_write(shdev, dmaor | shdev->pdata->dmaor_init);
+
+ dmaor = dmaor_read(shdev);
+
+ spin_unlock_irqrestore(&sh_dmae_lock, flags);
+
+ if (dmaor & (DMAOR_AE | DMAOR_NMIF)) {
+ dev_warn(shdev->common.dev, "Can't initialize DMAOR.\n");
+ return -EIO;
}
return 0;
}
@@ -184,7 +197,7 @@ static void dmae_init(struct sh_dmae_chan *sh_chan)

static int dmae_set_chcr(struct sh_dmae_chan *sh_chan, u32 val)
{
- /* When DMA was working, can not set data to CHCR */
+ /* If DMA is active, cannot set CHCR. TODO: remove this superfluous check */
if (dmae_is_busy(sh_chan))
return -EBUSY;

@@ -374,7 +387,12 @@ static void sh_dmae_free_chan_resources(struct dma_chan *chan)
LIST_HEAD(list);
int descs = sh_chan->descs_allocated;

+ /* Protect against ISR */
+ spin_lock_irq(&sh_chan->desc_lock);
dmae_halt(sh_chan);
+ spin_unlock_irq(&sh_chan->desc_lock);
+
+ /* Now no new interrupts will occur */

/* Prepared and not submitted descriptors can still be on the queue */
if (!list_empty(&sh_chan->ld_queue))
@@ -384,6 +402,7 @@ static void sh_dmae_free_chan_resources(struct dma_chan *chan)
/* The caller is holding dma_list_mutex */
struct sh_dmae_slave *param = chan->private;
clear_bit(param->slave_id, sh_dmae_slave_used);
+ chan->private = NULL;
}

spin_lock_bh(&sh_chan->desc_lock);
@@ -563,8 +582,6 @@ static struct dma_async_tx_descriptor *sh_dmae_prep_memcpy(
if (!chan || !len)
return NULL;

- chan->private = NULL;
-
sh_chan = to_sh_chan(chan);

sg_init_table(&sg, 1);
@@ -620,9 +637,9 @@ static int sh_dmae_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
if (!chan)
return -EINVAL;

+ spin_lock_bh(&sh_chan->desc_lock);
dmae_halt(sh_chan);

- spin_lock_bh(&sh_chan->desc_lock);
if (!list_empty(&sh_chan->ld_queue)) {
/* Record partial transfer */
struct sh_desc *desc = list_entry(sh_chan->ld_queue.next,
@@ -716,6 +733,14 @@ static dma_async_tx_callback __ld_cleanup(struct sh_dmae_chan *sh_chan, bool all
list_move(&desc->node, &sh_chan->ld_free);
}
}
+
+ if (all && !callback)
+ /*
+ * Terminating and the loop completed normally: forgive
+ * uncompleted cookies
+ */
+ sh_chan->completed_cookie = sh_chan->common.cookie;
+
spin_unlock_bh(&sh_chan->desc_lock);

if (callback)
@@ -733,10 +758,6 @@ static void sh_dmae_chan_ld_cleanup(struct sh_dmae_chan *sh_chan, bool all)
{
while (__ld_cleanup(sh_chan, all))
;
-
- if (all)
- /* Terminating - forgive uncompleted cookies */
- sh_chan->completed_cookie = sh_chan->common.cookie;
}

static void sh_chan_xfer_ld_queue(struct sh_dmae_chan *sh_chan)
@@ -782,8 +803,10 @@ static enum dma_status sh_dmae_tx_status(struct dma_chan *chan,

sh_dmae_chan_ld_cleanup(sh_chan, false);

- last_used = chan->cookie;
+ /* First read completed cookie to avoid a skew */
last_complete = sh_chan->completed_cookie;
+ rmb();
+ last_used = chan->cookie;
BUG_ON(last_complete < 0);
dma_set_tx_state(txstate, last_complete, last_used, 0);

@@ -813,8 +836,12 @@ static enum dma_status sh_dmae_tx_status(struct dma_chan *chan,
static irqreturn_t sh_dmae_interrupt(int irq, void *data)
{
irqreturn_t ret = IRQ_NONE;
- struct sh_dmae_chan *sh_chan = (struct sh_dmae_chan *)data;
- u32 chcr = sh_dmae_readl(sh_chan, CHCR);
+ struct sh_dmae_chan *sh_chan = data;
+ u32 chcr;
+
+ spin_lock(&sh_chan->desc_lock);
+
+ chcr = sh_dmae_readl(sh_chan, CHCR);

if (chcr & CHCR_TE) {
/* DMA stop */
@@ -824,10 +851,13 @@ static irqreturn_t sh_dmae_interrupt(int irq, void *data)
tasklet_schedule(&sh_chan->tasklet);
}

+ spin_unlock(&sh_chan->desc_lock);
+
return ret;
}

-static unsigned int sh_dmae_reset(struct sh_dmae_device *shdev)
+/* Called from error IRQ or NMI */
+static bool sh_dmae_reset(struct sh_dmae_device *shdev)
{
unsigned int handled = 0;
int i;
@@ -839,22 +869,32 @@ static unsigned int sh_dmae_reset(struct sh_dmae_device *shdev)
for (i = 0; i < SH_DMAC_MAX_CHANNELS; i++) {
struct sh_dmae_chan *sh_chan = shdev->chan[i];
struct sh_desc *desc;
+ LIST_HEAD(dl);

if (!sh_chan)
continue;

+ spin_lock(&sh_chan->desc_lock);
+
/* Stop the channel */
dmae_halt(sh_chan);

+ list_splice_init(&sh_chan->ld_queue, &dl);
+
+ spin_unlock(&sh_chan->desc_lock);
+
/* Complete all */
- list_for_each_entry(desc, &sh_chan->ld_queue, node) {
+ list_for_each_entry(desc, &dl, node) {
struct dma_async_tx_descriptor *tx = &desc->async_tx;
desc->mark = DESC_IDLE;
if (tx->callback)
tx->callback(tx->callback_param);
}

- list_splice_init(&sh_chan->ld_queue, &sh_chan->ld_free);
+ spin_lock(&sh_chan->desc_lock);
+ list_splice(&dl, &sh_chan->ld_free);
+ spin_unlock(&sh_chan->desc_lock);
+
handled++;
}

@@ -867,10 +907,11 @@ static irqreturn_t sh_dmae_err(int irq, void *data)
{
struct sh_dmae_device *shdev = data;

- if (dmaor_read(shdev) & DMAOR_AE)
- return IRQ_RETVAL(sh_dmae_reset(data));
- else
+ if (!(dmaor_read(shdev) & DMAOR_AE))
return IRQ_NONE;
+
+ sh_dmae_reset(data);
+ return IRQ_HANDLED;
}

static void dmae_do_tasklet(unsigned long data)
@@ -902,17 +943,11 @@ static void dmae_do_tasklet(unsigned long data)

static bool sh_dmae_nmi_notify(struct sh_dmae_device *shdev)
{
- unsigned int handled;
-
/* Fast path out if NMIF is not asserted for this controller */
if ((dmaor_read(shdev) & DMAOR_NMIF) == 0)
return false;

- handled = sh_dmae_reset(shdev);
- if (handled)
- return true;
-
- return false;
+ return sh_dmae_reset(shdev);
}

static int sh_dmae_nmi_handler(struct notifier_block *self,
@@ -982,9 +1017,6 @@ static int __devinit sh_dmae_chan_probe(struct sh_dmae_device *shdev, int id,
tasklet_init(&new_sh_chan->tasklet, dmae_do_tasklet,
(unsigned long)new_sh_chan);

- /* Init the channel */
- dmae_init(new_sh_chan);
-
spin_lock_init(&new_sh_chan->desc_lock);

/* Init descripter manage list */
@@ -1114,7 +1146,7 @@ static int __init sh_dmae_probe(struct platform_device *pdev)
list_add_tail_rcu(&shdev->node, &sh_dmae_devices);
spin_unlock_irq(&sh_dmae_lock);

- /* reset dma controller */
+ /* reset dma controller - only needed as a test */
err = sh_dmae_rst(shdev);
if (err)
goto rst_err;
--
1.7.2.5