On Fri, 17 Nov 2017 06:56:12 +0800 <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().
>
> Fix this by calculating pfn for linear and non-linear addresses.
>
It's a shame you didn't Cc Christoph, who was the sole reviewer of the
earlier version.
And it's a shame you didn't capture the result of that review
discussion in the v3 changelog.
And it's a shame that you didn't describe how this patch differs from
earlier versions.
Oh well, here's the incremental patch:
--- a/lib/dma-debug.c~dma-debug-fix-incorrect-pfn-calculation-v4
+++ a/lib/dma-debug.c
@@ -1495,15 +1495,22 @@ void debug_dma_alloc_coherent(struct dev
if (!entry)
return;
+ /* handle vmalloc and linear addresses */
+ if (!is_vmalloc_addr(virt) && !virt_to_page(virt))
+ return;
+
entry->type = dma_debug_coherent;
entry->dev = dev;
- 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;
entry->direction = DMA_BIDIRECTIONAL;
+ if (is_vmalloc_addr(virt))
+ entry->pfn = vmalloc_to_pfn(virt);
+ else
+ entry->pfn = page_to_pfn(virt_to_page(virt));
+
add_dma_entry(entry);
}
EXPORT_SYMBOL(debug_dma_alloc_coherent);
@@ -1514,14 +1521,21 @@ void debug_dma_free_coherent(struct devi
struct dma_debug_entry ref = {
.type = dma_debug_coherent,
.dev = dev,
- .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,
.direction = DMA_BIDIRECTIONAL,
};
+ /* handle vmalloc and linear addresses */
+ if (!is_vmalloc_addr(virt) && !virt_to_page(virt))
+ return;
+
+ if (is_vmalloc_addr(virt))
+ ref.pfn = vmalloc_to_pfn(virt);
+ else
+ ref.pfn = page_to_pfn(virt_to_page(virt));
+
if (unlikely(dma_debug_disabled()))
return;
_
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