Message ID | 20141218000357.GX11285@n2100.arm.linux.org.uk |
---|---|
State | RFC, archived |
Delegated to: | David Miller |
Headers | show |
On 12/17/2014 09:03 PM, Russell King - ARM Linux wrote: > On Wed, Dec 17, 2014 at 06:18:58PM -0300, Ezequiel Garcia wrote: >> On the other side, I haven't been able to reproduce this on my boards. I >> did try to put a hack to hold most lowmem pages, but it didn't make a >> difference. (In fact, I haven't been able to clearly see how the pages >> for the skbuff are allocated from high memory.) > > To be honest, I don't know either. All that I can do is describe what > happened... > > I've been running 3.17 since a week after it came out, and never saw a > problem there. > > Then I moved forward to 3.18, and ended up with memory corruption, which > seemed to be the GPU scribbling over kernel text (since the oops revealed > pixel values in the Code: line.) > > I thought it was a GPU problem - which seemed a reasonable assumption as > I know that the runtime PM I implemented for the GPU doesn't properly > restore the hardware state yet. So, I rebooted back into 3.18, this > time with all GPU users disabled, intending to download a kernel with > GPU runtime PM disabled. I'd also added additional debug to my X DDX > driver which logged the GPU command stream to a file on a NFS mount - > this does open(, O_CREAT|O_WRONLY|O_APPEND), write(), close() each > time it submits a block of commands. > > However, while my scripts to download the built kernel to the Cubox > were running, the kernel oopsed in the depths of dma_map_single() - the > kernel was trying to access a struct page for phys address 0x40000000, > which didn't exist. I decided to go back to 3.17 to get the updated > kernel on it, hoping that would sort it out. > > With the updated 3.18 kernel (with GPU runtime PM disabled), I found > that I'd still get oopses in from the network driver while X was starting > up, again from dma_map_single(). So, with all GPU users again disabled, > I set about debugging the this issue. > > I added a BUG_ON(!addr) after the page_address(), and that fired. I > added a BUG_ON(PageHighMem(this_frag->page.p)) and that fired too. > (Each time, I had to boot back to 3.17 in order to download the new > kernel, because very time I tried with 3.18, I'd hit this bug.) > > It's then when I reported the issue and asked the questions... > > I've since done a simple change, taking advantage that on ARM (or any > asm-generic/dma-mapping-common.h user), dma_unmap_single() and > dma_unmap_page() are the same function: > > diff --git a/drivers/net/ethernet/marvell/mv643xx_eth.c b/drivers/net/ethernet/marvell/mv643xx_eth.c > index d44560d1d268..c343ab03ab8b 100644 > --- a/drivers/net/ethernet/marvell/mv643xx_eth.c > +++ b/drivers/net/ethernet/marvell/mv643xx_eth.c > @@ -879,10 +879,8 @@ static void txq_submit_frag_skb(struct tx_queue *txq, struct sk_buff *skb) > skb_frag_t *this_frag; > int tx_index; > struct tx_desc *desc; > - void *addr; > > this_frag = &skb_shinfo(skb)->frags[frag]; > - addr = page_address(this_frag->page.p) + this_frag->page_offset; tx_index = txq->tx_curr_desc++; > if (txq->tx_curr_desc == txq->tx_ring_size) > txq->tx_curr_desc = 0; > @@ -902,8 +900,9 @@ static void txq_submit_frag_skb(struct tx_queue *txq, struct sk_buff *skb) > > desc->l4i_chk = 0; > desc->byte_cnt = skb_frag_size(this_frag); > - desc->buf_ptr = dma_map_single(mp->dev->dev.parent, addr, > - desc->byte_cnt, DMA_TO_DEVICE); > + desc->buf_ptr = skb_frag_dma_map(mp->dev->dev.parent, > + this_frag, 0, > + desc->byte_cnt, DMA_TO_DEVICE); } > } > > > I've been running that for the last five days, and I've yet to see > /any/ issues what so ever, and that includes running with the GPU > logging all that time: > > -rw-r--r-- 1 root root 17113616 Dec 17 23:52 /shared/etnaviv.bin > > During that time, I've been using the device over the network, running > various git commands, running builds, running the occasional build > via NFS, etc. > > So, for me it was trivially easy to reproduce (without my fix in place) > and all problems have gone away when I've fixed the apparent problem. > Well that's interesting. You've fixed only the non-TSO egress path, yet your original ethtool output showed tcp-segmentation-offload enabled. This seems to imply the highmem pages are found only for the non-TSO path. > However, exactly how it occurs, I don't know. My understanding from > reading the various feature flags was that NETIF_F_HIGHDMA was required > for highmem (see illegal_highdma()) so as this isn't set, we shouldn't > be seeing highmem fragments - which is why I asked the question in my > original email. > > If you want me to revert my fix above, and reproduce again, I can > certainly try that - or put a WARN_ON_ONCE(PageHighMem(this_frag->page.p)) > in there, but I seem to remember that it wasn't particularly useful as > the backtrace didn't show where the memory actually came from. > No, that's OK. Thanks a lot for all the details. I'll try to come up with a fix soon.
diff --git a/drivers/net/ethernet/marvell/mv643xx_eth.c b/drivers/net/ethernet/marvell/mv643xx_eth.c index d44560d1d268..c343ab03ab8b 100644 --- a/drivers/net/ethernet/marvell/mv643xx_eth.c +++ b/drivers/net/ethernet/marvell/mv643xx_eth.c @@ -879,10 +879,8 @@ static void txq_submit_frag_skb(struct tx_queue *txq, struct sk_buff *skb) skb_frag_t *this_frag; int tx_index; struct tx_desc *desc; - void *addr; this_frag = &skb_shinfo(skb)->frags[frag]; - addr = page_address(this_frag->page.p) + this_frag->page_offset; tx_index = txq->tx_curr_desc++; if (txq->tx_curr_desc == txq->tx_ring_size) txq->tx_curr_desc = 0; @@ -902,8 +900,9 @@ static void txq_submit_frag_skb(struct tx_queue *txq, struct sk_buff *skb)