Re: Question on kzalloc and GFP_DMA32

From: Ben Greear
Date: Wed Sep 28 2016 - 19:37:52 EST

On 09/28/2016 02:11 PM, David Rientjes wrote:
On Tue, 27 Sep 2016, Ben Greear wrote:

I have been running this patch for a while:

ath10k: Use GPF_DMA32 for firmware swap memory.

This fixes OS crash when using QCA 9984 NIC on x86-64 system
without vt-d enabled.

Also tested on ea8500 with 9980, and x86-64 with 9980 and 9880.

All tests were with CT firmware.

Signed-off-by: Ben Greear <greearb@xxxxxxxxxxxxxxx>

-------------------- drivers/net/wireless/ath/ath10k/wmi.c
index e20aa39..727b3aa 100644
@@ -4491,7 +4491,7 @@ static int ath10k_wmi_alloc_chunk(struct ath10k *ar, u32
if (!pool_size)
return -EINVAL;

- vaddr = kzalloc(pool_size, GFP_KERNEL | __GFP_NOWARN);
+ vaddr = kzalloc(pool_size, GFP_KERNEL | __GFP_NOWARN | GFP_DMA32);
if (!vaddr)
num_units /= 2;

It sometimes works, on some systems, but then it also often fails with the
below, especially with several NICs in the system.

I suppose it's failing sometimes because the BUG() will trigger when
trying to allocate new slab or CONFIG_ZONE_DMA32 isn't configured. That
shouldn't panic the kernel anymore since commit 72baeef0c271 ("slab: do
not panic on invalid gfp_mask") in 4.8, but you shouldn't be doing
kzalloc(..., ... | GFP_DMA32) anyway.

CONFIG_ZONE_DMA32 is enabled in my .config.

pool_size is relatively large (maybe 256k or so).

If it's 256k, why allocate through the slab allocator? Why not
alloc_pages(GFP_KERNEL | GFP_DMA32 | __GFP_ZERO | __GFP_NOWARN,

I really don't understand the (subtle?) difference between alloc_pages and kzalloc,
but I will give your suggestion a try and see if it works. If you have time, maybe you could take
a look at drivers/net/wireless/ath/ath10k/wmi.c in the ath10k_wmi_alloc_chunk method
to see if you notice any problems with using alloc_pages there?

Thanks for the suggestion.

Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc