dmaengine: shdma: fix locking

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

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 68 insertions, 36 deletions

diff --git a/drivers/dma/shdma.c b/drivers/dma/shdma.c
index d50da41ac328..727f51e903d9 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 */
@@ -1115,7 +1147,7 @@ static int __init sh_dmae_probe(struct platform_device *pdev)
         list_add_tail_rcu(&shdev->node, &sh_dmae_devices);
         spin_unlock_irqrestore(&sh_dmae_lock, flags);
 
-        /* reset dma controller */
+        /* reset dma controller - only needed as a test */
         err = sh_dmae_rst(shdev);
         if (err)
                 goto rst_err;