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SubjectRe: [PATCH 4/4] dma-mapping: clear dev->dma_ops in arch_teardown_dma_ops

On Mon, Aug 27, 2018 at 10:47:11AM +0200, Christoph Hellwig wrote:
> There is no reason to leave the per-device dma_ops around when
> deconfiguring a device, so move this code from arm64 into the
> common code.
> Signed-off-by: Christoph Hellwig <>
> Reviewed-by: Robin Murphy <>

This patch causes various ppc images to crash in -next due to NULL
DMA ops in dma_alloc_attrs().

Looking into the code, the macio driver tries to instantiate on
the 0000:f0:0d.0 PCI address (the driver maps to all Apple PCI IDs)
and fails. This results in a call to arch_teardown_dma_ops(). Later,
the same device pointer is used to instantiate ohci-pci, which
crashes in probe because the dma_ops pointer has been cleared.

I don't claim to fully understand the code, but to me it looks like
the pci device is allocated and waiting for a driver to attach to.
See arch/powerpc/kernel/pci_of_scan.c:of_create_pci_dev().
If attaching a driver (here: macio) fails, the same device pointer
is then reused for the next matching driver until a match is found
and the device is successfully instantiated. Of course this fails
quite badly if the device pointer has been scrubbed after the first

I don't know if this is generic PCI behavior or ppc specific.
I am copying pci and ppc maintainers for additional input.

Either case, reverting the patch fixes the problem.


ohci-pci 0000:f0:0d.0: OHCI PCI host controller
ohci-pci 0000:f0:0d.0: new USB bus registered, assigned bus number 1
------------[ cut here ]------------
kernel BUG at ./include/linux/dma-mapping.h:516!
Oops: Exception in kernel mode, sig: 5 [#1]
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W
4.19.0-rc4-next-20180921-dirty #1
NIP: c00000000086b824 LR: c00000000086b5dc CTR: c00000000086dd70
REGS: c00000003d30f0b0 TRAP: 0700 Tainted: G W
MSR: 800000000002b032 <SF,EE,FP,ME,IR,DR,RI> CR: 28008842 XER: 00000000
GPR00: c00000000086b5dc c00000003d30f330 c000000001199900 c00000003d3ce898
GPR04: c00000000115b798 c00000003d8c3a48 0000000000000000 0000000000000000
GPR08: 0000000000000000 ffffffffffffff00 0000000000000000 0000000000000020
GPR12: 0000000024008442 c000000001299000 c00000000000f720 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR24: 0000000000000000 c0000000010452e8 c000000001045420 0000000000000080
GPR28: 000000000000001c c000000001045408 c00000003d3ce898 c00000003d8c3a30
NIP [c00000000086b824] .ohci_init+0x564/0x570
LR [c00000000086b5dc] .ohci_init+0x31c/0x570
Call Trace:
[c00000003d30f330] [c00000000086b5dc] .ohci_init+0x31c/0x570 (unreliable)
[c00000003d30f3c0] [c00000000086de58] .ohci_pci_reset+0xa8/0xb0
[c00000003d30f440] [c0000000008335ec] .usb_add_hcd+0x35c/0x9b0
[c00000003d30f510] [c00000000084ea90] .usb_hcd_pci_probe+0x320/0x510
[c00000003d30f5c0] [c0000000006c7df8] .local_pci_probe+0x68/0x140
[c00000003d30f660] [c0000000006c92a4] .pci_device_probe+0x144/0x210
[c00000003d30f710] [c00000000074cd48] .really_probe+0x2a8/0x3c0
[c00000003d30f7b0] [c00000000074d100] .driver_probe_device+0x80/0x170
[c00000003d30f840] [c00000000074d33c] .__driver_attach+0x14c/0x150
[c00000003d30f8d0] [c000000000749c6c] .bus_for_each_dev+0xac/0x100
[c00000003d30f970] [c00000000074c334] .driver_attach+0x34/0x50
[c00000003d30f9f0] [c00000000074b9b8] .bus_add_driver+0x178/0x2f0
[c00000003d30fa90] [c00000000074e560] .driver_register+0x90/0x1a0
[c00000003d30fb10] [c0000000006c707c] .__pci_register_driver+0x6c/0x90
[c00000003d30fba0] [c000000000f39f14] .ohci_pci_init+0x90/0xac
[c00000003d30fc10] [c00000000000f380] .do_one_initcall+0x70/0x2d0
[c00000003d30fce0] [c000000000edfca4] .kernel_init_freeable+0x3b8/0x4b0
[c00000003d30fdb0] [c00000000000f744] .kernel_init+0x24/0x160
[c00000003d30fe30] [c00000000000b7a4] .ret_from_kernel_thread+0x58/0x74

# bad: [46c163a036b41a29b0ec3c475bf97515d755ff41] Add linux-next specific files for 20180921
# good: [7876320f88802b22d4e2daf7eb027dd14175a0f8] Linux 4.19-rc4
git bisect start 'HEAD' 'v4.19-rc4'
# bad: [03b5533c4d89cc558063a98fa4201a5d2b4eb1f7] Merge remote-tracking branch 'crypto/master'
git bisect bad 03b5533c4d89cc558063a98fa4201a5d2b4eb1f7
# bad: [62c54071a46255d59e26e95528b80bf432796cb4] Merge remote-tracking branch 'v9fs/9p-next'
git bisect bad 62c54071a46255d59e26e95528b80bf432796cb4
# bad: [1eee72bfcf0977daca74e9f902956adbb4f38847] Merge remote-tracking branch 'realtek/for-next'
git bisect bad 1eee72bfcf0977daca74e9f902956adbb4f38847
# good: [30d3220045f49c707bbeec1d35423bd60488c433] Merge remote-tracking branch 'scsi-fixes/fixes'
git bisect good 30d3220045f49c707bbeec1d35423bd60488c433
# bad: [a31a9772a2aa569dc279468da4be555b737e51f8] Merge remote-tracking branch 'at91/at91-next'
git bisect bad a31a9772a2aa569dc279468da4be555b737e51f8
# bad: [3f52a0ad91857e78a5feed28327eafa11c44412c] Merge remote-tracking branch 'arm-soc/for-next'
git bisect bad 3f52a0ad91857e78a5feed28327eafa11c44412c
# good: [92c76bf9685778b2b7e5d6b4c93d74d9ef5d54a7] Merge remote-tracking branch 'leaks/leaks-next'
git bisect good 92c76bf9685778b2b7e5d6b4c93d74d9ef5d54a7
# good: [4e7afff85160ffaa236785591126cf52e11f077c] Merge branch 'fixes' into for-next
git bisect good 4e7afff85160ffaa236785591126cf52e11f077c
# bad: [5748e1b35ba28368515d850e8087929a3a65e055] MIPS: don't select DMA_MAYBE_COHERENT from DMA_PERDEV_COHERENT
git bisect bad 5748e1b35ba28368515d850e8087929a3a65e055
# good: [ccf640f4c9988653ef884672381b03b9be247bec] dma-mapping: remove dma_configure
git bisect good ccf640f4c9988653ef884672381b03b9be247bec
# bad: [46053c73685411915d3de50c5a0045beef32806b] dma-mapping: clear dev->dma_ops in arch_teardown_dma_ops
git bisect bad 46053c73685411915d3de50c5a0045beef32806b
# good: [dc3c05504d38849f77149cb962caeaedd1efa127] dma-mapping: remove dma_deconfigure
git bisect good dc3c05504d38849f77149cb962caeaedd1efa127
# first bad commit: [46053c73685411915d3de50c5a0045beef32806b] dma-mapping: clear dev->dma_ops in arch_teardown_dma_ops

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