Messages in this thread | | | Subject | Re: [PATCH] USB: OHCI: ohci-sm501: complete URBs in BH context | From | Guenter Roeck <> | Date | Mon, 6 Aug 2018 08:58:07 -0700 |
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On 08/06/2018 01:33 AM, Christoph Hellwig wrote: > On Sun, Aug 05, 2018 at 02:38:22PM -0700, Guenter Roeck wrote: >> AFAICS it used to be interrupt tolerant for all but x86 up to commit >> 6894258eda ("dma-mapping: consolidate dma_{alloc,free}_{attrs,coherent}"). >> A quick test shows that the warning is indeed not seen if I run my test >> on v3.18.y. >> >> You would have to ask Christoph why it is now interrupt-intolerant for all >> architectures. > > interrupt-tolerant actually is a very odd wording. x86 itself (at least > unless using an iommu) actually is fine with calling dma_free_* with > interrupts disabled, but many other architectures are not. For many > architectures that are not cache coherent we'll have to manipulale > the kernel page tables when freeing coherent memory, which we absolutely > can't do from irq context. And as usual in the kernel we try to enforce > the same rules on everyone to allow for portable code. > > Also except for the odd USB use cases that abuses dma_alloc_coherent > for the bounce buffers in device local memory you are doing something > wrong if you call dma_alloc*/dma_free* anywhere but during device > initialization and removal. These are slow path interfaces for > allocating memory for things like descriptors and similar. Your fast > path should be using dma_map*/dma_unmap*. >
FWIW, that isn't "my" code. I just had the impunity to test it.
Cheers, Guenter
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