BASELINE RUN (stock X86_64_GENERIC kernel, INVARIANTS):

login: DF-5603: calling mmc_switch(timeout=0) as mmc.c does for a card with EXT_CSD[248]=0 ...
panic: mmc_switch: no timeout
cpuid = 1
Trace beginning at frame 0xfffff80118685728
mmc_switch() at mmc_switch+0x178 0xffffffff80573b08 
mmc_switch() at mmc_switch+0x178 0xffffffff80573b08 
df5603_modevent() at df5603_modevent+0x93 0xffffffff826000c3 
module_register_init() at module_register_init+0x49 0xffffffff806232e9 
linker_load_file.part.3() at linker_load_file.part.3+0x1b9 0xffffffff80624619 
linker_load_module() at linker_load_module+0x116 0xffffffff80625e16 
Debugger("panic")

CPU1 stopping CPUs: 0x0000003d
 stopped
Stopped at      Debugger+0x7c:  movb    $0,0xbdaf09(%rip)
db> 

(guest down; ssh session hung -> RUN timeout 124; vm.sh status => down)