Busybox `top` causes a SIGSEGV when run twice

[arihant2math]

bash-5.3# top
top: can't open 'stat': No such file or directory
bash-5.3# top
[    1.1358589] moss: Kernel panicked at src/sched/current.rs:59:13: Double mutable borrow of current task!

[arihant2math]

Also happens with ps, which makes me believe it's a problem with procfs.

[arihant2math]

Surprisingly this doesn't happen with the gnu coreutils ps, just the busybox ps. (Coreutils top needs nanosleep)

[arihant2math]

[    0.000000] arch::arm64::boot::memory: Adding memory region from FDT Px40000000 (0x80000000 bytes)
[    0.000000] arch::arm64::boot::memory: Reserving kernel text Px40080000 - Px41177000
[    0.000000] arch::arm64::boot::memory: Reserving FDT Px58000000 (0x100000 bytes)
[    0.000000] arch::arm64::boot::memory: Reserving initrd 0x48000000 - 0x58000000
[    0.000000] libkernel::memory::page_alloc: Buddy allocator initialized. Managing 524288 pages, 431104 free.
[    0.000000] drivers::fs::dev: devfs initialized
[    0.000000] drivers::interrupts::arm_gic_v3: ARM GICv3 found: dist @ <0x8000000, 0x10000>, rdist @ <0x80a0000, 0xf60000> (stride=0x20000)
[    0.000000] drivers::interrupts::arm_gic_v3: GICv3: Redistributor for core 0 (MPIDR=0x80000000) is awake.
[    0.000000] drivers::interrupts::arm_gic_v3: GICv3: CPU interface for core 0 enabled.
[    0.000000] interrupts: Setting device intc@8000000 as the interrupt root
[    0.000000] interrupts: Device timer claimed interrupt: Ppi(14)
[    0.001312] interrupts: Device pl011@9000000 claimed interrupt: Spi(1)
[    0.003305] libkernel::sync::per_cpu: Setup 12 per_cpu objects.
[    0.004023] interrupts: Device CPU Messenger claimed interrupt: Ipi(0)
[    0.004158] arch::arm64::proc::vdso: VDSO mapped to: 0xffff810000000000 (0x1000 bytes)
[    0.013255] drivers::fs::proc: procfs initialized
[    0.017385] drivers::interrupts::arm_gic_v3: GICv3: Redistributor for core 1 (MPIDR=0x80000001) is awake.
[    0.017590] drivers::interrupts::arm_gic_v3: GICv3: CPU interface for core 1 enabled.
[    0.017841] arch::arm64::boot::secondary: CPU 1 online.
[    0.018106] drivers::interrupts::arm_gic_v3: GICv3: Redistributor for core 2 (MPIDR=0x80000002) is awake.
[    0.018342] drivers::interrupts::arm_gic_v3: GICv3: CPU interface for core 2 enabled.
[    0.018531] arch::arm64::boot::secondary: CPU 2 online.
[    0.018828] drivers::interrupts::arm_gic_v3: GICv3: Redistributor for core 3 (MPIDR=0x80000003) is awake.
[    0.019006] drivers::interrupts::arm_gic_v3: GICv3: CPU interface for core 3 enabled.
[    0.019151] arch::arm64::boot::secondary: CPU 3 online.
bash-5.3# ps
PID   USER     TIME  COMMAND
    0 0         0:00 [idle]
    1 0         0:00 [/bin/bash]
    2 0         0:00 [busybox]
bash-5.3# ps
PID   USER     TIME  COMMAND
    0 0         0:00 [idle]
    1 0         0:00 [/bin/bash]
[    1.1151159] moss: Kernel panicked at src/arch/arm64/memory/fault.rs:125:13: SIGSEGV on process 3 DataAbortLowerEL(AbortIss { ifsc: Ifsc(6), write: true, far: Some(0) }) PC: 4e2a78

[arihant2math]

../../arm-gnu-toolchain/bin/aarch64-none-elf-objdump -d ext4_mount/bin/busybox | rg 4e2a78
  4e2a78:	3800275f 	strb	wzr, [x26], #2

Ok so a null pointer thing, perhaps some syscall is forgetting to modify something when it should?

Partial strace log:

bash-5.3# strace "/bin/busybox" "ps"
execve("/bin/busybox", ["/bin/busybox", "ps"], 0x7fffffffff38 /* 3 vars */) = 0
set_tid_address(0x561b88)               = 5
getuid()                                = 0
sysinfo({uptime=10, loads=[0, 0, 0], totalram=2147483648, freeram=1762369536, sharedram=0, bufferram=0, totalswap=0, freeswap=0, procs=6, totalhigh=0, freehigh=0, mem_unit=1}) = 0
brk(NULL)                               = 0x800000000000
brk(0x800000002000)                     = 0x800000002000
mmap(0x800000000000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x800000000000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fffff7ff000
ioctl(1, TIOCGWINSZ, {ws_row=33, ws_col=136, ws_xpixel=0, ws_ypixel=0}) = 0
ioctl(0, TIOCGWINSZ, {ws_row=33, ws_col=136, ws_xpixel=0, ws_ypixel=0}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fffff7fd000
ioctl(1, TIOCGWINSZ, {ws_row=33, ws_col=136, ws_xpixel=0, ws_ypixel=0}) = 0
writev(1, [{iov_base="PID   USER     TIME  COMMAND", iov_len=28}, {iov_base="\n", iov_len=1}], 2PID   USER     TIME  COMMAND
) = 29
openat(AT_FDCWD, "/proc", O_RDONLY|O_LARGEFILE|O_CLOEXEC|O_DIRECTORY) = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
getdents64(3, 0x7fffff7fdae8 /* 7 entries */, 2048) = 168
newfstatat(AT_FDCWD, "/proc/0/", {st_mode=S_IFDIR|0555, st_size=0, ...}, 0) = 0
openat(AT_FDCWD, "/proc/0/stat", O_RDONLY|O_LARGEFILE) = 4
read(4, "0 (idle) R 0 0 0 0 0 0 0 0 0 0 0"..., 1023) = 113
close(4)                                = 0
openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/proc/0/cmdline", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)
writev(1, [{iov_base="    0 0         0:00 [idle]", iov_len=27}, {iov_base="\n", iov_len=1}], 2    0 0         0:00 [idle]
) = 28
newfstatat(AT_FDCWD, "/proc/1/", {st_mode=S_IFDIR|0555, st_size=0, ...}, 0) = 0
openat(AT_FDCWD, "/proc/1/stat", O_RDONLY|O_LARGEFILE) = 4
read(4, "1 (/bin/bash) S 0 0 1 0 0 0 0 0 "..., 1023) = 115
close(4)                                = 0
openat(AT_FDCWD, "/proc/1/cmdline", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)
writev(1, [{iov_base="    1 0         0:00 [/bin/bash]", iov_len=32}, {iov_base="\n", iov_len=1}], 2    1 0         0:00 [/bin/bash]
) = 33
newfstatat(AT_FDCWD, "/proc/2/", {st_mode=S_IFDIR|0555, st_size=0, ...}, 0) = 0
openat(AT_FDCWD, "/proc/2/stat", O_RDONLY|O_LARGEFILE) = 4
read(4, "State:\tGone\n", 1023)         = 12
close(4)                                = 0
[   10.10142314] moss: Kernel panicked at src/arch/arm64/memory/fault.rs:125:13: SIGSEGV on process 5 DataAbortLowerEL(AbortIss { ifsc: Ifsc(6), write: true, far: Some(0) }) PC: 4e2a78