RE: [PATCH v6 5/8] fsl-dma: change release process of dmadescriptor for supporting async_tx

From: Liu Qiang-B32616
Date: Mon Aug 06 2012 - 23:22:28 EST

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> -----Original Message-----
> From: Ira W. Snyder [mailto:iws@xxxxxxxxxxxxxxxx]
> Sent: Tuesday, August 07, 2012 1:51 AM
> To: Liu Qiang-B32616
> Cc: linux-crypto@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> dan.j.williams@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> dan.j.williams@xxxxxxxxx; vinod.koul@xxxxxxxxx; arnd@xxxxxxxx;
> gregkh@xxxxxxxxxxxxxxxxxxx; herbert@xxxxxxxxxxxxxxxxxxxx;
> davem@xxxxxxxxxxxxx
> Subject: Re: [PATCH v6 5/8] fsl-dma: change release process of dma
> descriptor for supporting async_tx
>
> On Mon, Aug 06, 2012 at 06:14:33PM +0800, qiang.liu@xxxxxxxxxxxxx wrote:
> > From: Qiang Liu <qiang.liu@xxxxxxxxxxxxx>
> >
> > 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().
> >
> > 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
> >
> > Another modification in this patch is the change of completed
> descriptors,
> > there is a potential risk which caused by exception interrupt, all
> descriptors
> > in ld_running list are seemed completed when an interrupt raised, it
> works fine
> > under normal condition, but if there is an exception occured, it cannot
> work
> > as our excepted. Hardware should not be depend on s/w list, the right
> way is
> > to read current descriptor address register to find the last completed
> > descriptor. If an interrupt is raised by an error, all descriptors in
> ld_running
> > should not be seemed finished, or these unfinished descriptors in
> ld_running
> > will be released wrongly.
> >
> > A simple way to reproduce,
> > Enable dmatest first, then insert some bad descriptors which can
> trigger
> > Programming Error interrupts before the good descriptors. Last, the
> good
> > descriptors will be freed before they are processsed because of the
> exception
> > intrerrupt.
> >
> > Note: the bad descriptors are only for simulating an exception
> interrupt.
> > This case can illustrate the potential risk in current fsl-dma very
> well.
> >
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Vinod Koul <vinod.koul@xxxxxxxxx>
> > Cc: Li Yang <leoli@xxxxxxxxxxxxx>
> > Signed-off-by: Qiang Liu <qiang.liu@xxxxxxxxxxxxx>
> > Signed-off-by: Ira W. Snyder <iws@xxxxxxxxxxxxxxxx>
>
> There are two minor nitpicks below. Other than that, the patch looks
> excellent to me.
>
> Ira
>
> > ---
> > drivers/dma/fsldma.c | 232 ++++++++++++++++++++++++++++++++++--------
> --------
> > drivers/dma/fsldma.h | 17 +++-
> > 2 files changed, 174 insertions(+), 75 deletions(-)
> >
> > diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c
> > index 36490a3..938d8c1 100644
> > --- a/drivers/dma/fsldma.c
> > +++ b/drivers/dma/fsldma.c
> > @@ -472,6 +472,110 @@ static struct fsl_desc_sw
> *fsl_dma_alloc_descriptor(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 void
> > +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))
> > + fsl_dma_free_descriptor(chan, desc);
> > +}
> > +
> > +/**
> > + * fsldma_run_tx_complete_actions - cleanup 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 fsldma_chan
> *chan,
> > + struct fsl_desc_sw *desc, 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 void
> > +fsldma_clean_running_descriptor(struct fsldma_chan *chan,
> > + struct fsl_desc_sw *desc)
> > +{
> > + /* Remove from the list of transactions */
> > + list_del(&desc->node);
>
> Minor nitpick. Add a blank line here.
My fault. I will correct it.

>
> > + /*
> > + * 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;
> > + }
> > +
> > + dma_pool_free(chan->desc_pool, desc, desc->async_tx.phys);
> > +}
> > +
> > +/**
> > * fsl_chan_xfer_ld_queue - transfer any pending transactions
> > * @chan : Freescale DMA channel
> > *
> > @@ -539,51 +643,58 @@ static void fsl_chan_xfer_ld_queue(struct
> fsldma_chan *chan)
> > }
> >
> > /**
> > - * fsldma_cleanup_descriptor - cleanup and free a single link
> descriptor
> > + * fsldma_cleanup_descriptors - cleanup link descriptors which are
> completed
> > + * and move them to ld_completed to free until flag 'ack' is set
> > * @chan: Freescale DMA channel
> > - * @desc: descriptor to cleanup and free
> > *
> > - * This function is used on a descriptor which has been executed by
> the DMA
> > - * controller. It will run any callbacks, submit any dependencies, and
> then
> > - * free the descriptor.
> > + * This function is used on descriptors which have been executed by
> the DMA
> > + * controller. It will run any callbacks, submit any dependencies,
> then
> > + * free these descriptors if flag 'ack' is set.
> > */
> > -static void fsldma_cleanup_descriptor(struct fsldma_chan *chan,
> > - struct fsl_desc_sw *desc)
> > +static void fsldma_cleanup_descriptors(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 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 (!dma_is_idle(chan))
> > + break;
> > + }
>
> I wonder if this is better:
>
> if (desc->async_tx.phys == get_cdar(chan)) {
> seen_current = 1;
> if (!dma_is_idle(chan))
> break;
> }
>
> Your version works fine, it just might stop earlier than necessary. This
> is just a nitpick.
2 reasons make me cannot correct it as you expected in v6,
First, there is a conflict when we read current address register, dma devive will refill current address continually, there is an arbitration mechanism when we read this register, so it may not improve throughput.
Second, as I know, most normal interrupts means the whole list are completed but not for only single descriptor, so there should not be obvious improvement with the latest address. The current address is always same, it points the last descriptor of the list.
Sorry, I should explain it clearly in v5. Thanks.

>
> >
> > - /* 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);
> > + cookie = fsldma_run_tx_complete_actions(chan, desc, cookie);
> > +
> > + fsldma_clean_running_descriptor(chan, desc);
> > }
> >
> > - fsl_dma_free_descriptor(chan, desc);
> > + /*
> > + * 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;
> > }
> >
> > /**
> > @@ -654,8 +765,10 @@ 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_descriptors(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);
> > @@ -893,6 +1006,7 @@ static int fsl_dma_device_control(struct dma_chan
> *dchan,
> > /* Remove and free all of the descriptors in the LD queue */
> > fsldma_free_desc_list(chan, &chan->ld_pending);
> > fsldma_free_desc_list(chan, &chan->ld_running);
> > + fsldma_free_desc_list(chan, &chan->ld_completed);
> > chan->idle = true;
> >
> > spin_unlock_irqrestore(&chan->desc_lock, flags);
> > @@ -956,11 +1070,15 @@ 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_descriptors(chan);
> > spin_unlock_irqrestore(&chan->desc_lock, flags);
> >
> > - return ret;
> > + return dma_cookie_status(dchan, cookie, txstate);
> > }
> >
> > /*--------------------------------------------------------------------
> --------*/
> > @@ -1037,52 +1155,19 @@ 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 descriptors which have been completed */
> > + fsldma_cleanup_descriptors(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");
> > }
> > @@ -1264,6 +1349,7 @@ 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..a58275a 100644
> > --- a/drivers/dma/fsldma.h
> > +++ b/drivers/dma/fsldma.h
> > @@ -138,8 +138,21 @@ struct fsldma_chan {
> > char name[8]; /* Channel name */
> > struct fsldma_chan_regs __iomem *regs;
> > spinlock_t desc_lock; /* Descriptor operation lock */
> > - struct list_head ld_pending; /* Link descriptors queue */
> > - struct list_head ld_running; /* Link descriptors queue */
> > + /*
> > + * Descriptors which are queued to run, but have not yet been
> > + * submitted to the hardware for execution
> > + */
> > + struct list_head ld_pending;
> > + /*
> > + * Descriptors which are currently being executed by the hardware
> > + */
> > + struct list_head ld_running;
> > + /*
> > + * Descriptors which have finished execution by the hardware. These
> > + * descriptors have already had their cleanup actions run. They are
> > + * waiting for the ACK bit to be set by the async_tx API.
> > + */
> > + 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
> >
> >
> > _______________________________________________
> > Linuxppc-dev mailing list
> > Linuxppc-dev@xxxxxxxxxxxxxxxx
> > https://lists.ozlabs.org/listinfo/linuxppc-dev

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Next message: Liu Qiang-B32616: "RE: [PATCH v6 0/8] Raid: enable talitos xor offload for improvingperformance"
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