On 11/06, Jamie Iles wrote:
>
> I'm unable to reproduce the warning in qemu with SMP (on a 32 CPU VM).
Neither me. Perhaps because I tried this test-case on the minimal system
with /bin/sh running as init process.
> Instead I get the following instant traceback which is different to what
> you report when run as root:
>
> [ 45.018469] Kernel panic - not syncing: Attempted to kill init!
> exitcode=0x00000013
> [ 45.018469]
> [ 45.019669] CPU: 19 PID: 1 Comm: systemd Not tainted 4.14.0-rc8 #7
> [ 45.021094] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.10.1-1ubuntu1 04/01/2014
> [ 45.022768] Call Trace:
> [ 45.023076] dump_stack+0x12e/0x188
> [ 45.023481] panic+0x1e4/0x417
This is fine and hopefully confirms the theory. let me quote my previous email:
line 111 r[8] = syscall(__NR_ptrace, 0x10ul, r[7]);
this is PTRACE_ATTACH
line 115 syscall(__NR_ptrace, 0x4200ul, r[7],
0x40000012ul, 0x100012ul);
this is PTRACE_SETOPTIONS and "data" includes PTRACE_O_EXITKILL.
r[7] is initialized at
line 110 r[7] = *(uint32_t*)0x20f9cffc;
so if it is eq to 1 then it can attach to init and in this case the
problem
can be explained by the wrong SIGNAL_UNKILLABLE/SIGKILL logic.
So, if it is eq to 1 then init will be killed after the child process created
by loop() function exits (see PTRACE_O_EXITKILL above).
This is correct, only the warning is not.
For example, this command does ptrace(PTRACE_SEIZE, 1,0, PTRACE_O_EXITKILL)
# perl -e 'syscall 101, 0x4206, 1, 0, 0x100000'
and crashes the kernel the same way, this is correct.
Oleg.
