panic kexec broken on ARM64?

Petr Tesarik ptesarik at
Tue Jun 5 01:01:51 PDT 2018

Hi all,

I have observed hangs after crash on a Raspberry Pi 3 Model B+ board
when a panic kernel is loaded. I attached a hardware debugger and found
out that all CPU cores were stopped except one which was stuck in the
idle thread. It seems that irq_set_irqchip_state() may sleep, which is
definitely not safe after a kernel panic.

If I'm right, then this is broken in general, but I have only ever seen
it on RPi 3 Model B+ (even RPi3 Model B works fine), so the issue may
be more subtle. FWIW the code for 32-bit ARM seems to work just fine
without this code in machine_kexec_mask_interrupts():

                 * First try to remove the active state. If this
                 * fails, try to EOI the interrupt.
                ret = irq_set_irqchip_state(i, IRQCHIP_STATE_ACTIVE, false);

I wonder what breaks if this call to irq_set_irqchip_state() is removed.

For reference, here is a stack trace of the process which originally
triggered the panic:

#0  __switch_to (prev=0xffff000008e62a00 <init_task>, next=0xffff80002b796080) at ../arch/arm64/kernel/process.c:355
#1  0xffff0000088f584c in context_switch (rf=<optimized out>, next=<optimized out>, prev=<optimized out>, rq=<optimized out>) at ../kernel/sched/core.c:2896
#2  __schedule (preempt=false) at ../kernel/sched/core.c:3457
#3  0xffff0000088f5eac in schedule () at ../kernel/sched/core.c:3516
#4  0xffff0000088f9448 in schedule_timeout (timeout=<optimized out>) at ../kernel/time/timer.c:1743
#5  0xffff0000088f6afc in do_wait_for_common (state=<optimized out>, timeout=500, action=<optimized out>, x=<optimized out>) at ../kernel/sched/completion.c:77
#6  __wait_for_common (state=<optimized out>, timeout=<optimized out>, action=<optimized out>, x=<optimized out>) at ../kernel/sched/completion.c:96
#7  wait_for_common (x=0xffff000008e53848 <init_thread_union+14408>, timeout=500, state=<optimized out>) at ../kernel/sched/completion.c:104
#8  0xffff0000088f6c1c in wait_for_completion_timeout (x=0xffff000008e53848 <init_thread_union+14408>, timeout=500) at ../kernel/sched/completion.c:144
#9  0xffff000000a19f1c in usb_start_wait_urb (urb=0xffff80002c1cd700, timeout=5000, actual_length=0xffff000008e538dc <init_thread_union+14556>)
    at ../drivers/usb/core/message.c:61
#10 0xffff000000a1a05c in usb_internal_control_msg (timeout=<optimized out>, len=<optimized out>, data=<optimized out>, cmd=<optimized out>, pipe=<optimized out>, 
    usb_dev=<optimized out>) at ../drivers/usb/core/message.c:100
#11 usb_control_msg (dev=0xffff80002c348000, pipe=2147484800, request=161 '\241', requesttype=192 '\300', value=0, index=152, data=0xffff80002b6fa080, size=4, 
    timeout=5000) at ../drivers/usb/core/message.c:151
#12 0xffff000001001cd0 in lan78xx_read_reg (index=152, data=0xffff000008e5396c <init_thread_union+14700>, dev=<optimized out>, dev=<optimized out>)
    at ../drivers/net/usb/lan78xx.c:425
#13 0xffff00000100365c in lan78xx_irq_bus_sync_unlock (irqd=<optimized out>) at ../drivers/net/usb/lan78xx.c:1909
#14 0xffff00000813e590 in chip_bus_sync_unlock (desc=<optimized out>) at ../kernel/irq/internals.h:129
#15 __irq_put_desc_unlock (desc=0xffff80002c361c00, flags=128, bus=true) at ../kernel/irq/irqdesc.c:804
#16 0xffff00000813f604 in irq_put_desc_busunlock (flags=<optimized out>, desc=<optimized out>) at ../kernel/irq/internals.h:155
#17 irq_set_irqchip_state (irq=<optimized out>, which=<optimized out>, val=false) at ../kernel/irq/manage.c:2136
#18 0xffff00000809b7d4 in machine_kexec_mask_interrupts () at ../arch/arm64/kernel/machine_kexec.c:233
#19 machine_crash_shutdown (regs=<optimized out>) at ../arch/arm64/kernel/machine_kexec.c:259
#20 0xffff000008180fd4 in __crash_kexec (regs=0xffff000008e53d70 <init_thread_union+15728>) at ../kernel/kexec_core.c:943
#21 0xffff0000081810e4 in crash_kexec (regs=0xffff000008e53d70 <init_thread_union+15728>) at ../kernel/kexec_core.c:965
#22 0xffff00000808ab58 in die (str=<optimized out>, regs=0xffff000008e53d70 <init_thread_union+15728>, err=-2046820348) at ../arch/arm64/kernel/traps.c:266
#23 0xffff0000080a1c14 in __do_kernel_fault (mm=0x0, addr=0, esr=2248146948, regs=0xffff000008e53d70 <init_thread_union+15728>) at ../arch/arm64/mm/fault.c:226
#24 0xffff0000088fc8dc in do_page_fault (addr=0, esr=2248146948, regs=0xffff000008e53d70 <init_thread_union+15728>) at ../arch/arm64/mm/fault.c:476
#25 0xffff0000088fccdc in do_translation_fault (addr=0, esr=2248146948, regs=0xffff000008e53d70 <init_thread_union+15728>) at ../arch/arm64/mm/fault.c:502
#26 0xffff000008081478 in do_mem_abort (addr=0, esr=2248146948, regs=0xffff000008e53d70 <init_thread_union+15728>) at ../arch/arm64/mm/fault.c:657
#27 0xffff000008082dd0 in el1_sync () at ../arch/arm64/kernel/entry.S:548

Petr T

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