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async_tx: remove walk of tx->parent chain in dma_wait_for_async_tx

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We currently walk the parent chain when waiting for a given tx to
complete however this walk may race with the driver cleanup routine.
The routines in async_raid6_recov.c may fall back to the synchronous
path at any point so we need to be prepared to call async_tx_quiesce()
(which calls  dma_wait_for_async_tx).  To remove the ->parent walk we
guarantee that every time a dependency is attached ->issue_pending() is
invoked, then we can simply poll the initial descriptor until
completion.

This also allows for a lighter weight 'issue pending' implementation as
there is no longer a requirement to iterate through all the channels'
->issue_pending() routines as long as operations have been submitted in
an ordered chain.  async_tx_issue_pending() is added for this case.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams
2009-07-14 12:19:02 -07:00
parent af1f951eb6
commit 95475e5711
3 changed files with 40 additions and 41 deletions
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45
drivers/dma/dmaengine.c
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@@ -934,49 +934,24 @@ EXPORT_SYMBOL(dma_async_tx_descriptor_init);
/* dma_wait_for_async_tx - spin wait for a transaction to complete
* @tx: in-flight transaction to wait on
*
* This routine assumes that tx was obtained from a call to async_memcpy,
* async_xor, async_memset, etc which ensures that tx is "in-flight" (prepped
* and submitted). Walking the parent chain is only meant to cover for DMA
* drivers that do not implement the DMA_INTERRUPT capability and may race with
* the driver's descriptor cleanup routine.
*/
enum dma_status
dma_wait_for_async_tx(struct dma_async_tx_descriptor *tx)
{
enum dma_status status;
struct dma_async_tx_descriptor *iter;
struct dma_async_tx_descriptor *parent;
unsigned long dma_sync_wait_timeout = jiffies + msecs_to_jiffies(5000);
if (!tx)
return DMA_SUCCESS;
WARN_ONCE(tx->parent, "%s: speculatively walking dependency chain for"
" %s\n", __func__, dma_chan_name(tx->chan));
/* poll through the dependency chain, return when tx is complete */
do {
iter = tx;
/* find the root of the unsubmitted dependency chain */
do {
parent = iter->parent;
if (!parent)
break;
else
iter = parent;
} while (parent);
/* there is a small window for ->parent == NULL and
* ->cookie == -EBUSY
*/
while (iter->cookie == -EBUSY)
cpu_relax();
status = dma_sync_wait(iter->chan, iter->cookie);
} while (status == DMA_IN_PROGRESS || (iter != tx));
return status;
while (tx->cookie == -EBUSY) {
if (time_after_eq(jiffies, dma_sync_wait_timeout)) {
pr_err("%s timeout waiting for descriptor submission\n",
__func__);
return DMA_ERROR;
}
cpu_relax();
}
return dma_sync_wait(tx->chan, tx->cookie);
}
EXPORT_SYMBOL_GPL(dma_wait_for_async_tx);