Johannes, On Mon, 2008-11-17 at 16:47 -0800, Johannes Berg wrote: > [patch below, sorry for the long list of CCs] > > 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@xxxxxxxxxxxxxxxx> > --- Above you mention that this patch fixes bug #11596. Could you please explain how this patch addresses that problem? A short summary of the bug is that no data (ping packets) can be transmitted while station is associated. We have, what appears to be, a similar bug in our bug tracking system (http://www.intellinuxwireless.org/bugzilla/show_bug.cgi?id=1807 ), but this patch was not able to resolve this issue. Bug #11596 was recently closed after the user tested with 2.6.27.4, which does not have this patch. Thank you Reinette -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
