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SubjectKernel panic while doing vfio-pci hot-plug/unplug test
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Hi all,

Recently I encountered a kernel panic while doing vfio-pci hot-plug/unplug test repeatly on my Arm-KVM virtual machines.
See the call stack below:

[66628.697280] vfio-pci 0000:06:03.5: enabling device (0000 -> 0002)
[66628.809290] vfio-pci 0000:06:03.1: enabling device (0000 -> 0002)
[66628.921283] vfio-pci 0000:06:02.7: enabling device (0000 -> 0002)
[66629.029280] vfio-pci 0000:06:03.6: enabling device (0000 -> 0002)
[66629.137338] vfio-pci 0000:06:03.2: enabling device (0000 -> 0002)
[66629.249285] vfio-pci 0000:06:03.7: enabling device (0000 -> 0002)
[66630.237261] Unable to handle kernel read from unreadable memory at virtual address ffff802dac469000
[66630.246266] Mem abort info:
[66630.249047] ESR = 0x8600000d
[66630.252088] Exception class = IABT (current EL), IL = 32 bits
[66630.257981] SET = 0, FnV = 0
[66630.261022] EA = 0, S1PTW = 0
[66630.264150] swapper pgtable: 4k pages, 48-bit VAs, pgdp = 00000000fb16886e
[66630.270992] [ffff802dac469000] pgd=0000203fffff6803, pud=00e8002d80000f11
[66630.277751] Internal error: Oops: 8600000d [#1] SMP
[66630.282606] Process qemu-kvm (pid: 37201, stack limit = 0x00000000d8f19858)
[66630.289537] CPU: 41 PID: 37201 Comm: qemu-kvm Kdump: loaded Tainted: G OE 4.19.36-vhulk1907.1.0.h453.eulerosv2r8.aarch64 #1
[66630.301822] Hardware name: Huawei TaiShan 2280 V2/BC82AMDDA, BIOS 0.88 07/24/2019
[66630.309270] pstate: 80400089 (Nzcv daIf +PAN -UAO)
[66630.314042] pc : 0xffff802dac469000
[66630.317519] lr : __wake_up_common+0x90/0x1a8
[66630.321768] sp : ffff00027746bb00
[66630.325067] x29: ffff00027746bb00 x28: 0000000000000000
[66630.330355] x27: 0000000000000000 x26: ffff0000092755b8
[66630.335643] x25: 0000000000000000 x24: 0000000000000000
[66630.340930] x23: 0000000000000003 x22: ffff00027746bbc0
[66630.346219] x21: 000000000954c000 x20: ffff0001f542bc6c
[66630.351506] x19: ffff0001f542bb90 x18: 0000000000000000
[66630.356793] x17: 0000000000000000 x16: 0000000000000000
[66630.362081] x15: 0000000000000000 x14: 0000000000000000
[66630.367368] x13: 0000000000000000 x12: 0000000000000000
[66630.372655] x11: 0000000000000000 x10: 0000000000000bb0
[66630.377942] x9 : ffff00027746ba50 x8 : ffff80367ff6ca10
[66630.383229] x7 : ffff802e20d59200 x6 : 000000000000003f
[66630.388517] x5 : ffff00027746bbc0 x4 : ffff802dac469000
[66630.393806] x3 : 0000000000000000 x2 : 0000000000000000
[66630.399093] x1 : 0000000000000003 x0 : ffff0001f542bb90
[66630.404381] Call trace:
[66630.406818] 0xffff802dac469000
[66630.409945] __wake_up_common_lock+0xa8/0x1a0
[66630.414283] __wake_up+0x40/0x50
[66630.417499] pci_cfg_access_unlock+0x9c/0xd0
[66630.421752] pci_try_reset_function+0x58/0x78
[66630.426095] vfio_pci_ioctl+0x478/0xdb8 [vfio_pci]
[66630.430870] vfio_device_fops_unl_ioctl+0x44/0x70 [vfio]
[66630.436158] do_vfs_ioctl+0xc4/0x8c0
[66630.439718] ksys_ioctl+0x8c/0xa0
[66630.443018] __arm64_sys_ioctl+0x28/0x38
[66630.446925] el0_svc_common+0x78/0x130
[66630.450657] el0_svc_handler+0x38/0x78
[66630.454389] el0_svc+0x8/0xc
[66630.457260] Code: 00000000 00000000 00000000 00000000 (ac46d000)
[66630.463325] kernel fault(0x1) notification starting on CPU 41
[66630.469044] kernel fault(0x1) notification finished on CPU 41

The chance to reproduce this problem is very small. We had an initial analysis of this problem,
and found it was caused by the illegal value of the 'curr->func' in the __wake_up_common() function.

I cannot image how 'curr->func' can be wrote to 0xffff802dac469000. Is there any problem about
concurrent competition between the pci_wait_cfg() function and the wake_up_all() function?


--

Thanks,
Xiang

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