[patch 14/22] iwlagn: fix RX skb alignment

Greg KH
2008-12-17T00:09:11Z

[-- Attachment #1: iwlagn-fix-rx-skb-alignment.patch --]
[-- Type: text/plain, Size: 5919 bytes --]

2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Johannes Berg <johannes@sipsolutions.net>

commit 4018517a1a69a85c3d61b20fa02f187b80773137 upstream.

So I dug deeper into the DMA problems I had with iwlagn and a kind soul
helped me in that he said something about pci-e alignment and mentioned
the iwl_rx_allocate function to check for crossing 4KB boundaries. Since
there's 8KB A-MPDU support, crossing 4k boundaries didn't seem like
something the device would fail with, but when I looked into the
function for a minute anyway I stumbled over this little gem:

BUG_ON(rxb->dma_addr & (~DMA_BIT_MASK(36) & 0xff));

Clearly, that is a totally bogus check, one would hope the compiler
removes it entirely. (Think about it)

After fixing it, I obviously ran into it, nothing guarantees the
alignment the way you want it, because of the way skbs and their
headroom are allocated. I won't explain that here nor double-check that
I'm right, that goes beyond what most of the CC'ed people care about.

So then I came up with the patch below, and so far my system has
survived minutes with 64K pages, when it would previously fail in
seconds. And I haven't seen a single instance of the TX bug either. But
when you see the patch it'll be pretty obvious to you why.

This should fix the following reported kernel bugs:

http://bugzilla.kernel.org/show_bug.cgi?id=11596
http://bugzilla.kernel.org/show_bug.cgi?id=11393
http://bugzilla.kernel.org/show_bug.cgi?id=11983

I haven't checked if there are any elsewhere, but I suppose RHBZ will
have a few instances too...

I'd like to ask anyone who is CC'ed (those are people I know ran into
the bug) to try this patch.

I am convinced that this patch is correct in spirit, but I haven't
understood why, for example, there are so many unmap calls. I'm not
entirely convinced that this is the only bug leading to the TX reply
errors.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/net/wireless/iwlwifi/iwl-agn.c | 6 +++---
drivers/net/wireless/iwlwifi/iwl-dev.h | 3 ++-
drivers/net/wireless/iwlwifi/iwl-rx.c | 26 +++++++++++++++++---------
3 files changed, 22 insertions(+), 13 deletions(-)

--- a/drivers/net/wireless/iwlwifi/iwl-agn.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn.c
@@ -1384,7 +1384,7 @@ void iwl_rx_handle(struct iwl_priv *priv

rxq->queue[i] = NULL;

- pci_dma_sync_single_for_cpu(priv->pci_dev, rxb->dma_addr,
+ pci_dma_sync_single_for_cpu(priv->pci_dev, rxb->aligned_dma_addr,
priv->hw_params.rx_buf_size,
PCI_DMA_FROMDEVICE);
pkt = (struct iwl_rx_packet *)rxb->skb->data;
@@ -1436,8 +1436,8 @@ void iwl_rx_handle(struct iwl_priv *priv
rxb->skb = NULL;
}

- pci_unmap_single(priv->pci_dev, rxb->dma_addr,
- priv->hw_params.rx_buf_size,
+ pci_unmap_single(priv->pci_dev, rxb->real_dma_addr,
+ priv->hw_params.rx_buf_size + 256,
PCI_DMA_FROMDEVICE);
spin_lock_irqsave(&rxq->lock, flags);
list_add_tail(&rxb->list, &priv->rxq.rx_used);
--- a/drivers/net/wireless/iwlwifi/iwl-dev.h
+++ b/drivers/net/wireless/iwlwifi/iwl-dev.h
@@ -89,7 +89,8 @@ extern struct iwl_cfg iwl5100_abg_cfg;
#define DEFAULT_LONG_RETRY_LIMIT 4U

struct iwl_rx_mem_buffer {
- dma_addr_t dma_addr;
+ dma_addr_t real_dma_addr;
+ dma_addr_t aligned_dma_addr;
struct sk_buff *skb;
struct list_head list;
};
--- a/drivers/net/wireless/iwlwifi/iwl-rx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-rx.c
@@ -204,7 +204,7 @@ int iwl_rx_queue_restock(struct iwl_priv
list_del(element);

/* Point to Rx buffer via next RBD in circular buffer */
- rxq->bd[rxq->write] = iwl_dma_addr2rbd_ptr(priv, rxb->dma_addr);
+ rxq->bd[rxq->write] = iwl_dma_addr2rbd_ptr(priv, rxb->aligned_dma_addr);
rxq->queue[rxq->write] = rxb;
rxq->write = (rxq->write + 1) & RX_QUEUE_MASK;
rxq->free_count--;
@@ -251,7 +251,7 @@ void iwl_rx_allocate(struct iwl_priv *pr
rxb = list_entry(element, struct iwl_rx_mem_buffer, list);

/* Alloc a new receive buffer */
- rxb->skb = alloc_skb(priv->hw_params.rx_buf_size,
+ rxb->skb = alloc_skb(priv->hw_params.rx_buf_size + 256,
__GFP_NOWARN | GFP_ATOMIC);
if (!rxb->skb) {
if (net_ratelimit())
@@ -266,9 +266,17 @@ void iwl_rx_allocate(struct iwl_priv *pr
list_del(element);

/* Get physical address of RB/SKB */
- rxb->dma_addr =
- pci_map_single(priv->pci_dev, rxb->skb->data,
- priv->hw_params.rx_buf_size, PCI_DMA_FROMDEVICE);
+ rxb->real_dma_addr = pci_map_single(
+ priv->pci_dev,
+ rxb->skb->data,
+ priv->hw_params.rx_buf_size + 256,
+ PCI_DMA_FROMDEVICE);
+ /* dma address must be no more than 36 bits */
+ BUG_ON(rxb->real_dma_addr & ~DMA_BIT_MASK(36));
+ /* and also 256 byte aligned! */
+ rxb->aligned_dma_addr = ALIGN(rxb->real_dma_addr, 256);
+ skb_reserve(rxb->skb, rxb->aligned_dma_addr - rxb->real_dma_addr);
+
list_add_tail(&rxb->list, &rxq->rx_free);
rxq->free_count++;
}
@@ -300,8 +308,8 @@ void iwl_rx_queue_free(struct iwl_priv *
for (i = 0; i < RX_QUEUE_SIZE + RX_FREE_BUFFERS; i++) {
if (rxq->pool[i].skb != NULL) {
pci_unmap_single(priv->pci_dev,
- rxq->pool[i].dma_addr,
- priv->hw_params.rx_buf_size,
+ rxq->pool[i].real_dma_addr,
+ priv->hw_params.rx_buf_size + 256,
PCI_DMA_FROMDEVICE);
dev_kfree_skb(rxq->pool[i].skb);
}
@@ -354,8 +362,8 @@ void iwl_rx_queue_reset(struct iwl_priv
* to an SKB, so we need to unmap and free potential storage */
if (rxq->pool[i].skb != NULL) {
pci_unmap_single(priv->pci_dev,
- rxq->pool[i].dma_addr,
- priv->hw_params.rx_buf_size,
+ rxq->pool[i].real_dma_addr,
+ priv->hw_params.rx_buf_size + 256,
PCI_DMA_FROMDEVICE);
priv->alloc_rxb_skb--;
dev_kfree_skb(rxq->pool[i].skb);