Subject: Re: [PATCH v4 3/7] fsl-dma: change release process of dma descriptor for supporting async_tx

From: "Ira W. Snyder" <[email-masked]>
Date: Mon, 30 Jul 2012 14:10:05 -0700

On Fri, Jul 27, 2012 at 05:16:09PM +0800, [email-masked] wrote:
> From: Qiang Liu <[email-masked]>
> 
> Fix the potential risk when enable config NET_DMA and ASYNC_TX.
> Async_tx is lack of support in current release process of dma descriptor,
> all descriptors will be released whatever is acked or no-acked by async_tx,
> so there is a potential race condition when dma engine is uesd by others
> clients (e.g. when enable NET_DMA to offload TCP).
> 
> In our case, a race condition which is raised when use both of talitos
> and dmaengine to offload xor is because napi scheduler will sync all
> pending requests in dma channels, it affects the process of raid operations
> due to ack_tx is not checked in fsl dma. The no-acked descriptor is freed
> which is submitted just now, as a dependent tx, this freed descriptor trigger
> BUG_ON(async_tx_test_ack(depend_tx)) in async_tx_submit().
> 

I'm preparing an alternative version of this patch that I think is
easier to understand (it is much shorter). I'll post it up here as soon
as I finish testing.

It would be nice to know how to easily reproduce this bug, without
needing to set up a RAID system. I don't have access to any such
hardware. A driver similar to drivers/dma/dmatest.c (using the async_tx
API instead) would be wonderful.

Thanks,
Ira

> TASK = ee1a94a0[1390] 'md0_raid5' THREAD: ecf40000 CPU: 0
> GPR00: 00000001 ecf41ca0 ee44/921a94a0 0000003f 00000001 c00593e4 00000000 00000001
> GPR08: 00000000 a7a7a7a7 00000001 045/920000002 42028042 100a38d4 ed576d98 00000000
> GPR16: ed5a11b0 00000000 2b162000 00000200 046/920000000 2d555000 ed3015e8 c15a7aa0
> GPR24: 00000000 c155fc40 00000000 ecb63220 ecf41d28 e47/92f640bb0 ef640c30 ecf41ca0
> NIP [c02b048c] async_tx_submit+0x6c/0x2b4
> LR [c02b068c] async_tx_submit+0x26c/0x2b4
> Call Trace:
> [ecf41ca0] [c02b068c] async_tx_submit+0x26c/0x2b448/92 (unreliable)
> [ecf41cd0] [c02b0a4c] async_memcpy+0x240/0x25c
> [ecf41d20] [c0421064] async_copy_data+0xa0/0x17c
> [ecf41d70] [c0421cf4] __raid_run_ops+0x874/0xe10
> [ecf41df0] [c0426ee4] handle_stripe+0x820/0x25e8
> [ecf41e90] [c0429080] raid5d+0x3d4/0x5b4
> [ecf41f40] [c04329b8] md_thread+0x138/0x16c
> [ecf41f90] [c008277c] kthread+0x8c/0x90
> [ecf41ff0] [c0011630] kernel_thread+0x4c/0x68
> 
> Cc: Dan Williams <[email-masked]>
> Cc: Vinod Koul <[email-masked]>
> Cc: Li Yang <[email-masked]>
> Cc: Ira W. Snyder <[email-masked]>
> Signed-off-by: Qiang Liu <[email-masked]>
> ---
>  drivers/dma/fsldma.c |  242 +++++++++++++++++++++++++++++++++++---------------
>  drivers/dma/fsldma.h |    1 +
>  2 files changed, 172 insertions(+), 71 deletions(-)
> 
> diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c
> index 4f2f212..87f52c0 100644
> --- a/drivers/dma/fsldma.c
> +++ b/drivers/dma/fsldma.c
> @@ -400,6 +400,125 @@ out_splice:
>  	list_splice_tail_init(&desc->tx_list, &chan->ld_pending);
>  }
> 
> +static void fsldma_cleanup_descriptor(struct fsldma_chan *chan);
> +static void fsl_chan_xfer_ld_queue(struct fsldma_chan *chan);
> +
> +/**
> + * fsldma_clean_completed_descriptor - free all descriptors which
> + * has been completed and acked
> + * @chan: Freescale DMA channel
> + *
> + * This function is used on all completed and acked descriptors.
> + * All descriptors should only be freed in this function.
> + */
> +static int
> +fsldma_clean_completed_descriptor(struct fsldma_chan *chan)
> +{
> +	struct fsl_desc_sw *desc, *_desc;
> +
> +	/* Run the callback for each descriptor, in order */
> +	list_for_each_entry_safe(desc, _desc, &chan->ld_completed, node) {
> +
> +		if (async_tx_test_ack(&desc->async_tx)) {
> +			/* Remove from the list of transactions */
> +			list_del(&desc->node);
> +#ifdef FSL_DMA_LD_DEBUG
> +			chan_dbg(chan, "LD %p free\n", desc);
> +#endif
> +			dma_pool_free(chan->desc_pool, desc,
> +					desc->async_tx.phys);
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * fsldma_run_tx_complete_actions - cleanup and free a single link descriptor
> + * @chan: Freescale DMA channel
> + * @desc: descriptor to cleanup and free
> + * @cookie: Freescale DMA transaction identifier
> + *
> + * This function is used on a descriptor which has been executed by the DMA
> + * controller. It will run any callbacks, submit any dependencies.
> + */
> +static dma_cookie_t fsldma_run_tx_complete_actions(struct fsl_desc_sw *desc,
> +		struct fsldma_chan *chan, dma_cookie_t cookie)
> +{
> +	struct dma_async_tx_descriptor *txd = &desc->async_tx;
> +	struct device *dev = chan->common.device->dev;
> +	dma_addr_t src = get_desc_src(chan, desc);
> +	dma_addr_t dst = get_desc_dst(chan, desc);
> +	u32 len = get_desc_cnt(chan, desc);
> +
> +	BUG_ON(txd->cookie < 0);
> +
> +	if (txd->cookie > 0) {
> +		cookie = txd->cookie;
> +
> +		/* Run the link descriptor callback function */
> +		if (txd->callback) {
> +#ifdef FSL_DMA_LD_DEBUG
> +			chan_dbg(chan, "LD %p callback\n", desc);
> +#endif
> +			txd->callback(txd->callback_param);
> +		}
> +
> +		/* Unmap the dst buffer, if requested */
> +		if (!(txd->flags & DMA_COMPL_SKIP_DEST_UNMAP)) {
> +			if (txd->flags & DMA_COMPL_DEST_UNMAP_SINGLE)
> +				dma_unmap_single(dev, dst, len, DMA_FROM_DEVICE);
> +			else
> +				dma_unmap_page(dev, dst, len, DMA_FROM_DEVICE);
> +		}
> +
> +		/* Unmap the src buffer, if requested */
> +		if (!(txd->flags & DMA_COMPL_SKIP_SRC_UNMAP)) {
> +			if (txd->flags & DMA_COMPL_SRC_UNMAP_SINGLE)
> +				dma_unmap_single(dev, src, len, DMA_TO_DEVICE);
> +			else
> +				dma_unmap_page(dev, src, len, DMA_TO_DEVICE);
> +		}
> +	}
> +
> +	/* Run any dependencies */
> +	dma_run_dependencies(txd);
> +
> +	return cookie;
> +}
> +
> +/**
> + * fsldma_clean_running_descriptor - move the completed descriptor from
> + * ld_running to ld_completed
> + * @chan: Freescale DMA channel
> + * @desc: the descriptor which is completed
> + *
> + * Free the descriptor directly if acked by async_tx api, or move it to
> + * queue ld_completed.
> + */
> +static int
> +fsldma_clean_running_descriptor(struct fsldma_chan *chan,
> +		struct fsl_desc_sw *desc)
> +{
> +	/* Remove from the list of transactions */
> +	list_del(&desc->node);
> +	/*
> +	 * the client is allowed to attach dependent operations
> +	 * until 'ack' is set
> +	 */
> +	if (!async_tx_test_ack(&desc->async_tx)) {
> +		/*
> +		 * Move this descriptor to the list of descriptors which is
> +		 * completed, but still awaiting the 'ack' bit to be set.
> +		 */
> +		list_add_tail(&desc->node, &chan->ld_completed);
> +		return 0;
> +	}
> +
> +	dma_pool_free(chan->desc_pool, desc, desc->async_tx.phys);
> +	return 0;
> +}
> +
>  static dma_cookie_t fsl_dma_tx_submit(struct dma_async_tx_descriptor *tx)
>  {
>  	struct fsldma_chan *chan = to_fsl_chan(tx->chan);
> @@ -534,8 +653,10 @@ static void fsl_dma_free_chan_resources(struct dma_chan *dchan)
> 
>  	chan_dbg(chan, "free all channel resources\n");
>  	spin_lock_irqsave(&chan->desc_lock, flags);
> +	fsldma_cleanup_descriptor(chan);
>  	fsldma_free_desc_list(chan, &chan->ld_pending);
>  	fsldma_free_desc_list(chan, &chan->ld_running);
> +	fsldma_free_desc_list(chan, &chan->ld_completed);
>  	spin_unlock_irqrestore(&chan->desc_lock, flags);
> 
>  	dma_pool_destroy(chan->desc_pool);
> @@ -819,46 +940,53 @@ static int fsl_dma_device_control(struct dma_chan *dchan,
>   * controller. It will run any callbacks, submit any dependencies, and then
>   * free the descriptor.
>   */
> -static void fsldma_cleanup_descriptor(struct fsldma_chan *chan,
> -				      struct fsl_desc_sw *desc)
> +static void fsldma_cleanup_descriptor(struct fsldma_chan *chan)
>  {
> -	struct dma_async_tx_descriptor *txd = &desc->async_tx;
> -	struct device *dev = chan->common.device->dev;
> -	dma_addr_t src = get_desc_src(chan, desc);
> -	dma_addr_t dst = get_desc_dst(chan, desc);
> -	u32 len = get_desc_cnt(chan, desc);
> +	struct fsl_desc_sw *desc, *_desc;
> +	dma_cookie_t cookie = 0;
> +	dma_addr_t curr_phys = get_cdar(chan);
> +	int idle = dma_is_idle(chan);
> +	int seen_current = 0;
> 
> -	/* Run the link descriptor callback function */
> -	if (txd->callback) {
> -#ifdef FSL_DMA_LD_DEBUG
> -		chan_dbg(chan, "LD %p callback\n", desc);
> -#endif
> -		txd->callback(txd->callback_param);
> -	}
> +	fsldma_clean_completed_descriptor(chan);
> 
> -	/* Run any dependencies */
> -	dma_run_dependencies(txd);
> +	/* Run the callback for each descriptor, in order */
> +	list_for_each_entry_safe(desc, _desc, &chan->ld_running, node) {
> +		/*
> +		 * do not advance past the current descriptor loaded into the
> +		 * hardware channel, subsequent descriptors are either in
> +		 * process or have not been submitted
> +		 */
> +		if (seen_current)
> +			break;
> 
> -	/* Unmap the dst buffer, if requested */
> -	if (!(txd->flags & DMA_COMPL_SKIP_DEST_UNMAP)) {
> -		if (txd->flags & DMA_COMPL_DEST_UNMAP_SINGLE)
> -			dma_unmap_single(dev, dst, len, DMA_FROM_DEVICE);
> -		else
> -			dma_unmap_page(dev, dst, len, DMA_FROM_DEVICE);
> -	}
> +		/*
> +		 * stop the search if we reach the current descriptor and the
> +		 * channel is busy
> +		 */
> +		if (desc->async_tx.phys == curr_phys) {
> +			seen_current = 1;
> +			if (!idle)
> +				break;
> +		}
> +
> +		cookie = fsldma_run_tx_complete_actions(desc, chan, cookie);
> +
> +		if (fsldma_clean_running_descriptor(chan, desc))
> +			break;
> 
> -	/* Unmap the src buffer, if requested */
> -	if (!(txd->flags & DMA_COMPL_SKIP_SRC_UNMAP)) {
> -		if (txd->flags & DMA_COMPL_SRC_UNMAP_SINGLE)
> -			dma_unmap_single(dev, src, len, DMA_TO_DEVICE);
> -		else
> -			dma_unmap_page(dev, src, len, DMA_TO_DEVICE);
>  	}
> 
> -#ifdef FSL_DMA_LD_DEBUG
> -	chan_dbg(chan, "LD %p free\n", desc);
> -#endif
> -	dma_pool_free(chan->desc_pool, desc, txd->phys);
> +	/*
> +	 * Start any pending transactions automatically
> +	 *
> +	 * In the ideal case, we keep the DMA controller busy while we go
> +	 * ahead and free the descriptors below.
> +	 */
> +	fsl_chan_xfer_ld_queue(chan);
> +
> +	if (cookie > 0)
> +		chan->common.completed_cookie = cookie;
>  }
> 
>  /**
> @@ -954,11 +1082,15 @@ static enum dma_status fsl_tx_status(struct dma_chan *dchan,
>  	enum dma_status ret;
>  	unsigned long flags;
> 
> -	spin_lock_irqsave(&chan->desc_lock, flags);
>  	ret = dma_cookie_status(dchan, cookie, txstate);
> +	if (ret == DMA_SUCCESS)
> +		return ret;
> +
> +	spin_lock_irqsave(&chan->desc_lock, flags);
> +	fsldma_cleanup_descriptor(chan);
>  	spin_unlock_irqrestore(&chan->desc_lock, flags);
> 
> -	return ret;
> +	return dma_cookie_status(dchan, cookie, txstate);
>  }
> 
>  /*----------------------------------------------------------------------------*/
> @@ -1035,52 +1167,19 @@ static irqreturn_t fsldma_chan_irq(int irq, void *data)
>  static void dma_do_tasklet(unsigned long data)
>  {
>  	struct fsldma_chan *chan = (struct fsldma_chan *)data;
> -	struct fsl_desc_sw *desc, *_desc;
> -	LIST_HEAD(ld_cleanup);
>  	unsigned long flags;
> 
>  	chan_dbg(chan, "tasklet entry\n");
> 
>  	spin_lock_irqsave(&chan->desc_lock, flags);
> 
> -	/* update the cookie if we have some descriptors to cleanup */
> -	if (!list_empty(&chan->ld_running)) {
> -		dma_cookie_t cookie;
> -
> -		desc = to_fsl_desc(chan->ld_running.prev);
> -		cookie = desc->async_tx.cookie;
> -		dma_cookie_complete(&desc->async_tx);
> -
> -		chan_dbg(chan, "completed_cookie=%d\n", cookie);
> -	}
> -
> -	/*
> -	 * move the descriptors to a temporary list so we can drop the lock
> -	 * during the entire cleanup operation
> -	 */
> -	list_splice_tail_init(&chan->ld_running, &ld_cleanup);
> -
>  	/* the hardware is now idle and ready for more */
>  	chan->idle = true;
> 
> -	/*
> -	 * Start any pending transactions automatically
> -	 *
> -	 * In the ideal case, we keep the DMA controller busy while we go
> -	 * ahead and free the descriptors below.
> -	 */
> -	fsl_chan_xfer_ld_queue(chan);
> -	spin_unlock_irqrestore(&chan->desc_lock, flags);
> -
> -	/* Run the callback for each descriptor, in order */
> -	list_for_each_entry_safe(desc, _desc, &ld_cleanup, node) {
> +	/* Run all cleanup for this descriptor */
> +	fsldma_cleanup_descriptor(chan);
> 
> -		/* Remove from the list of transactions */
> -		list_del(&desc->node);
> -
> -		/* Run all cleanup for this descriptor */
> -		fsldma_cleanup_descriptor(chan, desc);
> -	}
> +	spin_unlock_irqrestore(&chan->desc_lock, flags);
> 
>  	chan_dbg(chan, "tasklet exit\n");
>  }
> @@ -1262,6 +1361,7 @@ static int __devinit fsl_dma_chan_probe(struct fsldma_device *fdev,
>  	spin_lock_init(&chan->desc_lock);
>  	INIT_LIST_HEAD(&chan->ld_pending);
>  	INIT_LIST_HEAD(&chan->ld_running);
> +	INIT_LIST_HEAD(&chan->ld_completed);
>  	chan->idle = true;
> 
>  	chan->common.device = &fdev->common;
> diff --git a/drivers/dma/fsldma.h b/drivers/dma/fsldma.h
> index f5c3879..7ede908 100644
> --- a/drivers/dma/fsldma.h
> +++ b/drivers/dma/fsldma.h
> @@ -140,6 +140,7 @@ struct fsldma_chan {
>  	spinlock_t desc_lock;		/* Descriptor operation lock */
>  	struct list_head ld_pending;	/* Link descriptors queue */
>  	struct list_head ld_running;	/* Link descriptors queue */
> +	struct list_head ld_completed;	/* Link descriptors queue */
>  	struct dma_chan common;		/* DMA common channel */
>  	struct dma_pool *desc_pool;	/* Descriptors pool */
>  	struct device *dev;		/* Channel device */
> --
> 1.7.5.1
> 
>