From 95475e57113c66aac7583925736ed2e2d58c990d Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Tue, 14 Jul 2009 12:19:02 -0700 Subject: [PATCH] async_tx: remove walk of tx->parent chain in dma_wait_for_async_tx 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 --- crypto/async_tx/async_tx.c | 13 +++++++------ drivers/dma/dmaengine.c | 45 ++++++++++----------------------------------- include/linux/async_tx.h | 23 +++++++++++++++++++++++ 3 files changed, 40 insertions(+), 41 deletions(-) diff --git a/crypto/async_tx/async_tx.c b/crypto/async_tx/async_tx.c index 6e37ad3..60615fe 100644 --- a/crypto/async_tx/async_tx.c +++ b/crypto/async_tx/async_tx.c @@ -77,8 +77,8 @@ static void async_tx_channel_switch(struct dma_async_tx_descriptor *depend_tx, struct dma_async_tx_descriptor *tx) { - struct dma_chan *chan; - struct dma_device *device; + struct dma_chan *chan = depend_tx->chan; + struct dma_device *device = chan->device; struct dma_async_tx_descriptor *intr_tx = (void *) ~0; /* first check to see if we can still append to depend_tx */ @@ -90,11 +90,11 @@ async_tx_channel_switch(struct dma_async_tx_descriptor *depend_tx, } spin_unlock_bh(&depend_tx->lock); - if (!intr_tx) + /* attached dependency, flush the parent channel */ + if (!intr_tx) { + device->device_issue_pending(chan); return; - - chan = depend_tx->chan; - device = chan->device; + } /* see if we can schedule an interrupt * otherwise poll for completion @@ -128,6 +128,7 @@ async_tx_channel_switch(struct dma_async_tx_descriptor *depend_tx, intr_tx->tx_submit(intr_tx); async_tx_ack(intr_tx); } + device->device_issue_pending(chan); } else { if (dma_wait_for_async_tx(depend_tx) == DMA_ERROR) panic("%s: DMA_ERROR waiting for depend_tx\n", diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 6781e8f..e002e0e 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -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); diff --git a/include/linux/async_tx.h b/include/linux/async_tx.h index 3d21a25..12a2efc 100644 --- a/include/linux/async_tx.h +++ b/include/linux/async_tx.h @@ -83,6 +83,24 @@ struct async_submit_ctl { #ifdef CONFIG_DMA_ENGINE #define async_tx_issue_pending_all dma_issue_pending_all + +/** + * async_tx_issue_pending - send pending descriptor to the hardware channel + * @tx: descriptor handle to retrieve hardware context + * + * Note: any dependent operations will have already been issued by + * async_tx_channel_switch, or (in the case of no channel switch) will + * be already pending on this channel. + */ +static inline void async_tx_issue_pending(struct dma_async_tx_descriptor *tx) +{ + if (likely(tx)) { + struct dma_chan *chan = tx->chan; + struct dma_device *dma = chan->device; + + dma->device_issue_pending(chan); + } +} #ifdef CONFIG_ARCH_HAS_ASYNC_TX_FIND_CHANNEL #include #else @@ -98,6 +116,11 @@ static inline void async_tx_issue_pending_all(void) do { } while (0); } +static inline void async_tx_issue_pending(struct dma_async_tx_descriptor *tx) +{ + do { } while (0); +} + static inline struct dma_chan * async_tx_find_channel(struct async_submit_ctl *submit, enum dma_transaction_type tx_type, struct page **dst, -- 1.8.2.3