i.MX6 PCIe bug (scheduling while atomic)

EricNelson — Sat, 31 May 2014 17:47:33 GMT

We got a very nice bug report from Naoki Aizu on our Github repository:

imx6_pcie_link_up: scheduling while atomic · Issue #9 · boundarydevices/linux-imx6 · GitHub

The details are also there, but the PCI_OP_WRITE macro is calling the imx6_pcie_link_up() routine while holding an IRQ spinlock. Since imx6_pcie_link_up() calls usleep_range(), this results in the following kernel message:

PCI: enabling device 0000:01:00.0 (0140 -> 0142)
BUG: scheduling while atomic: udevd/163/0x00000002
Modules linked in: ath9k(+) ath9k_common ath9k_hw ath
CPU: 0 PID: 163 Comm: udevd Not tainted 3.10.17-1.0.0-wandboard-02558-g41aacad #13
[<80014600>] (unwind_backtrace+0x0/0xf8) from [<80011460>] (show_stack+0x10/0x14)
[<80011460>] (show_stack+0x10/0x14) from [<8065d720>] (__schedule_bug+0x44/0x5c)
[<8065d720>] (__schedule_bug+0x44/0x5c) from [<80663340>] (__schedule+0x4e4/0x58c)
[<80663340>] (__schedule+0x4e4/0x58c) from [<80662780>] (schedule_hrtimeout_range_clock+0xd8/0x144)
[<80662780>] (schedule_hrtimeout_range_clock+0xd8/0x144) from [<80033d84>] (usleep_range+0x48/0x50)
[<80033d84>] (usleep_range+0x48/0x50) from [<802a24d8>] (imx6_pcie_link_up+0x38/0x150)
[<802a24d8>] (imx6_pcie_link_up+0x38/0x150) from [<802a1898>] (dw_pcie_valid_config.isra.3+0x3c/0x8c)
[<802a1898>] (dw_pcie_valid_config.isra.3+0x3c/0x8c) from [<802a1bc0>] (dw_pcie_wr_conf+0x3c/0xf8)
[<802a1bc0>] (dw_pcie_wr_conf+0x3c/0xf8) from [<80291fdc>] (pci_bus_write_config_word+0x60/0x78)
[<80291fdc>] (pci_bus_write_config_word+0x60/0x78) from [<802950c4>] (__pci_set_master+0x50/0x64)
[<802950c4>] (__pci_set_master+0x50/0x64) from [<80298380>] (pci_set_master+0x10/0x1c)
[<80298380>] (pci_set_master+0x10/0x1c) from [<7f081bfc>] (ath_pci_probe+0xe4/0x2b4 [ath9k])
[<7f081bfc>] (ath_pci_probe+0xe4/0x2b4 [ath9k]) from [<80299750>] (pci_device_probe+0x74/0xac)
[<80299750>] (pci_device_probe+0x74/0xac) from [<8031b56c>] (driver_probe_device+0x104/0x214)
[<8031b56c>] (driver_probe_device+0x104/0x214) from [<8031b708>] (__driver_attach+0x8c/0x90)
[<8031b708>] (__driver_attach+0x8c/0x90) from [<80319da4>] (bus_for_each_dev+0x54/0x88)
[<80319da4>] (bus_for_each_dev+0x54/0x88) from [<8031ac90>] (bus_add_driver+0xd8/0x228)
[<8031ac90>] (bus_add_driver+0xd8/0x228) from [<8031bbbc>] (driver_register+0x78/0x144)
[<8031bbbc>] (driver_register+0x78/0x144) from [<7f088008>] (ath9k_init+0x8/0x2c [ath9k])
[<7f088008>] (ath9k_init+0x8/0x2c [ath9k]) from [<8000862c>] (do_one_initcall+0x34/0x15c)
[<8000862c>] (do_one_initcall+0x34/0x15c) from [<8006b8b0>] (load_module+0x1a44/0x1e5c)
[<8006b8b0>] (load_module+0x1a44/0x1e5c) from [<8006be10>] (SyS_finit_module+0x68/0x6c)
[<8006be10>] (SyS_finit_module+0x68/0x6c) from [<8000e080>] (ret_fast_syscall+0x0/0x30)
ieee80211 phy0: Atheros AR9462 Rev:2 mem=0xc0c00000, irq=155
=======================

This bug appears in all of the Freescale kernels we've looked at including the 3.10.31_1.1.0_alpha:

pci/access.c linux-2.6-imx.git - Freescale i.MX Linux Tree

pci/host/pci-imx6.c linux-2.6-imx.git - Freescale i.MX Linux Tree

It appears that the delay is needed, so it's not clear how this should be addressed.

Re: i.MX6 PCIe bug (scheduling while atomic)

jamesbone — Mon, 02 Jun 2014 15:54:35 GMT

Dear Eric,

Our expert team it is reviewing your issue privatly , we will provide an answer soon.

Re: i.MX6 PCIe bug (scheduling while atomic)

EricNelson — Mon, 02 Jun 2014 17:18:38 GMT

Thanks James

Re: i.MX6 PCIe bug (scheduling while atomic)

b47504 — Thu, 05 Jun 2014 06:09:45 GMT

Comments from Richard:

The sleep should be replaced by the delay if it maybe used in the irq-context.

Re: i.MX6 PCIe bug (scheduling while atomic)

EricNelson — Thu, 05 Jun 2014 16:53:21 GMT

Thanks Yuan (and Richard).

I'm not in a position to test, but hopefully provided the right info to Naoki:

imx6_pcie_link_up: scheduling while atomic · Issue #9 · boundarydevices/linux-imx6 · GitHub

Re: i.MX6 PCIe bug (scheduling while atomic)

EricNelson — Sat, 07 Jun 2014 15:51:54 GMT

To close this out, it appears that changing the usleep_range() to udelay() addresses the issue:

imx6_pcie_link_up: scheduling while atomic · Issue #9 · boundarydevices/linux-imx6 · GitHub

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i.MX6 PCIe bug (scheduling while atomic)

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