Subject: powerpc: DMA coherent allocations broken for CONFIG_NOT_COHERENT_CACHE

From: Albert Herranz <[email-masked]>
Date: Thu, 21 May 2009 16:50:23 +0000 (GMT)

Hello list,

Commit 33f00dcedb0e22cdb156a23632814fc580fcfcf8 seems to have broken DMA coherent allocations for CONFIG_NOT_COHERENT_CACHE platforms.

The problems seem to be that the new __dma_alloc_coherent() and __dma_free_coherent() implementations:

- don't respect anymore the passed gfp flags (__dma_alloc_coherent() unconditionally uses GFP_KERNEL within the function irrespective of the caller flags)
- can't be used in interrupt context as they use get_vm_area_caller()/vfree() which end up triggering BUG_ON(in_interrupt())

One victim happens to be the USB core subsystem which sometimes frees dma coherent memory in interrupt context for drivers flagged HCD_LOCAL_MEM.

This has been experienced while writing a new EHCI driver for the Nintendo Wii platform.

usb 1-1: new high speed USB device using ehci-mipc and address 2
------------[ cut here ]------------
kernel BUG at mm/vmalloc.c:1328!
Oops: Exception in kernel mode, sig: 5 [#1]
PREEMPT wii
Modules linked in:
NIP: c008ea20 LR: c0015890 CTR: c00111d4
REGS: d2c65b10 TRAP: 0700   Not tainted  (2.6.30-rc2-isobel-wii-00092-gcba94db-dirty)
MSR: 00021032 <ME,CE,IR,DR>  CR: 42482028  XER: 00000000
TASK = d2c600f0[28] 'kmmcd' THREAD: d2c64000
GPR00: 00010000 d2c65bc0 d2c600f0 d4030000 d4030000 d4030000 12da1000 00000001 
GPR08: 00000000 d2c64000 00000020 00000000 22482022 94fdfb98 6e1979bc c6bbdbdd 
GPR16: 00000020 00200200 00100100 d4020060 00000001 d401c0ec 00000001 d401c0ec 
GPR24: d2d9a6c0 00000000 00000000 d2f69de0 d2d9a600 d2f69e30 d2f69e2c d2da08e0 
NIP [c008ea20] vfree+0xc/0x18
LR [c0015890] __dma_free_coherent+0x14/0x24
Call Trace:
[d2c65bc0] [c0017af8] __mipc_recv_req+0x160/0x178 (unreliable)
[d2c65bd0] [c00111ec] dma_direct_free_coherent+0x18/0x28
[d2c65be0] [c01cfca4] hcd_free_coherent+0x7c/0x12c
[d2c65c10] [c01d00b8] unmap_urb_for_dma+0x150/0x1cc
[d2c65c20] [c01d0174] usb_hcd_giveback_urb+0x40/0xe4
[d2c65c30] [c01df474] ehci_urb_done+0xf0/0x114
[d2c65c50] [c01e3870] qh_completions+0x41c/0x4dc
[d2c65ca0] [c01e44e0] scan_async+0x9c/0x1a0
[d2c65cc0] [c01e49ec] ehci_work+0x58/0xc4
[d2c65cd0] [c01e5424] ehci_irq+0x22c/0x230
[d2c65d00] [c01cfa88] usb_hcd_irq+0x50/0xa8
[d2c65d20] [c00597d8] handle_IRQ_event+0xdc/0x250
[d2c65d60] [c005ba20] handle_level_irq+0x9c/0x138
[d2c65d80] [c001cbc8] hollywood_pic_irq_cascade+0x7c/0xf8
[d2c65da0] [c00064b4] do_IRQ+0x9c/0xc4
[d2c65dc0] [c0011fb8] ret_from_except+0x0/0x14

Any comments on how to address this issue (other than reverting the above mentioned commit, which fixes it) are welcome.

Thanks,
Albert