Hi Marek,
On Tue, 21 Aug 2012 17:01:08 +0200 Marek Szyprowski m.szyprowski@samsung.com wrote:
-__iommu_alloc_remap(struct page **pages, size_t size, gfp_t gfp, pgprot_t prot) +__iommu_alloc_remap(struct page **pages, size_t size, gfp_t gfp, pgprot_t prot,
const void *caller){
struct arm_vmregion *c;size_t align;size_t count = size >> PAGE_SHIFT;int bit;
unsigned int i, nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;struct vm_struct *area;unsigned long p;
if (!consistent_pte[0]) {pr_err("%s: not initialised\n", __func__);dump_stack();
area = get_vm_area_caller(size, VM_ARM_DMA_CONSISTENT | VM_USERMAP,caller);if (!area)This patch replaced the custom "consistent_pte" with get_vm_area_caller()", which breaks the compatibility with the existing driver. This causes the following kernel oops(*1). That driver has called dma_pool_alloc() to allocate memory from the interrupt context, and it hits BUG_ON(in_interrpt()) in "get_vm_area_caller()"(*2). Regardless of the badness of allocation from interrupt handler in the driver, I have the following question.
The following "__get_vm_area_node()" can take gfp_mask, it means that this function is expected to be called from atomic context, but why it's _NOT_ allowed _ONLY_ from interrupt context?
According to the following definitions, "in_interrupt()" is in "in_atomic()".
#define in_interrupt() (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK | NMI_MASK)) #define in_atomic() ((preempt_count() & ~PREEMPT_ACTIVE) != 0)
Does anyone know why BUG_ON(in_interrupt()) is set in __get_vm_area_node(*3)?
For arm_dma_alloc(), it allocates from the pool if GFP_ATOMIC, but for arm_iommu_alloc_attrs() doesn't have pre-allocate pool at all, and it always call "get_vm_area_caller()". That's why it hits BUG(). But still I don't understand why it's not BUG_ON(in_atomic) as Russell already pointed out(*1).
Ok, now I see the problem. I will try to find out a solution for your issue.
My explanation wasn't so good.
For a solution, I thought that, in order to allow IOMMU'able device drivers to allocate memory from atomic context/ISR, there were the following 2 solutions:
(1) To provide the pre-allocate area like arm_dma_alloc() does, or (2) __get_vm_area_node() can be called from ISR.
But (2) doesn't work because PGALLOC_GFP(GFP_KERNEL) is used to allocate a page table. This is called from:
arm_iommu_alloc_attrs() -> __iommu_alloc_remap() -> ioremap_page_range() -> ..... -> pte_alloc_one_kernel() -> pte = (pte_t *)__get_free_page(PGALLOC_GFP);
We always have to avoid changing a page table for atomic allocation. So for me, the only remaining solution is (1) pre-allocation. We can make use of the same atomic pool both for DMA and IOMMU. I'll send the patch.