iommu/arm-smmu: Regression (sleeping function called from invalid context)

On Fri, Jan 31, 2014 at 12:55:52AM +0100, Andreas Herrmann wrote:

Hi Will,

Seems that commit a44a9791e778d9ccda50d5534028ed4057a9a45b
(iommu/arm-smmu: use mutex instead of spinlock for locking page tables)
introduced a regression.

At least I've hit

  BUG: scheduling while atomic: ksoftirqd/0/3/0x00000100
...

  BUG: sleeping function called from invalid context at mm/page_alloc.c:2679
  in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/0
  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.13.0-00016-g6e90346 #413
  [<c0014740>] (unwind_backtrace+0x0/0xf8) from [<c00115b0>] (show_stack+0x10/0x14)
  [<c00115b0>] (show_stack+0x10/0x14) from [<c057ea24>] (dump_stack+0x74/0xa8)
  [<c057ea24>] (dump_stack+0x74/0xa8) from [<c00acc1c>] (__alloc_pages_nodemask+0x174/0x930)
  [<c00acc1c>] (__alloc_pages_nodemask+0x174/0x930) from [<c042a250>] (arm_smmu_handle_mapping+0x470/0x66c)
  [<c042a250>] (arm_smmu_handle_mapping+0x470/0x66c) from [<c0428e74>] (iommu_map+0xf0/0x148)
  [<c0428e74>] (iommu_map+0xf0/0x148) from [<c001935c>] (__map_sg_chunk+0x198/0x2d4)
...

Maybe that was the reason why the offending commit was introduced(?).

I think with the current code "atomic allocations" should be used when
IO page tables are created. With below patch I've not triggered above
errors.

I think allocating memory with GFP_KERNEL in this dma-mapping path
doesn't seem to be a good idea. What if the DMA operation for which we
modify IO page tables was triggered to free pages (page cache, swap)?


Andreas