[+DMA maintainers]
On 27/09/17 04:48, miles.chen@xxxxxxxxxxxx wrote:
> From: Miles Chen <miles.chen@xxxxxxxxxxxx>
>
> dma-debug reports the following warning:
>
> [name:panic&]WARNING: CPU: 3 PID: 298 at kernel-4.4/lib/dma-debug.c:604
> debug _dma_assert_idle+0x1a8/0x230()
> DMA-API: cpu touching an active dma mapped cacheline [cln=0x00000882300]
> CPU: 3 PID: 298 Comm: vold Tainted: G W O 4.4.22+ #1
> Hardware name: MT6739 (DT)
> Call trace:
> [<ffffff800808acd0>] dump_backtrace+0x0/0x1d4
> [<ffffff800808affc>] show_stack+0x14/0x1c
> [<ffffff800838019c>] dump_stack+0xa8/0xe0
> [<ffffff80080a0594>] warn_slowpath_common+0xf4/0x11c
> [<ffffff80080a061c>] warn_slowpath_fmt+0x60/0x80
> [<ffffff80083afe24>] debug_dma_assert_idle+0x1a8/0x230
> [<ffffff80081dca9c>] wp_page_copy.isra.96+0x118/0x520
> [<ffffff80081de114>] do_wp_page+0x4fc/0x534
> [<ffffff80081e0a14>] handle_mm_fault+0xd4c/0x1310
> [<ffffff8008098798>] do_page_fault+0x1c8/0x394
> [<ffffff800808231c>] do_mem_abort+0x50/0xec
>
> I found that debug_dma_alloc_coherent() and debug_dma_free_coherent()
> assume that dma_alloc_coherent() always returns a linear address.
> However it's possible that dma_alloc_coherent() returns a non-linear
> address. In this case, page_to_pfn(virt_to_page(virt)) will return an
> incorrect pfn. If the pfn is valid and mapped as a COW page,
> we will hit the warning when doing wp_page_copy().
Yeah, we definitely want that explanation recorded in the commit, since
the warning is pretty non-obvious otherwise.
Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
> Fix this by calculating pfn for linear and non-linear addresses.
>
> Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx>
> ---
> lib/dma-debug.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/lib/dma-debug.c b/lib/dma-debug.c
> index ea4cc3d..e5b4237 100644
> --- a/lib/dma-debug.c
> +++ b/lib/dma-debug.c
> @@ -1497,7 +1497,8 @@ void debug_dma_alloc_coherent(struct device *dev, size_t size,
>
> entry->type = dma_debug_coherent;
> entry->dev = dev;
> - entry->pfn = page_to_pfn(virt_to_page(virt));
> + entry->pfn = is_vmalloc_addr(virt) ? vmalloc_to_pfn(virt) :
> + page_to_pfn(virt_to_page(virt));
> entry->offset = offset_in_page(virt);
> entry->size = size;
> entry->dev_addr = dma_addr;
> @@ -1513,7 +1514,8 @@ void debug_dma_free_coherent(struct device *dev, size_t size,
> struct dma_debug_entry ref = {
> .type = dma_debug_coherent,
> .dev = dev,
> - .pfn = page_to_pfn(virt_to_page(virt)),
> + .pfn = is_vmalloc_addr(virt) ? vmalloc_to_pfn(virt) :
> + page_to_pfn(virt_to_page(virt)),
> .offset = offset_in_page(virt),
> .dev_addr = addr,
> .size = size,
>
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