On Mon, Jun 21, 2021 at 03:18:35PM +1200, Michael Schmitz wrote: > This is what I get from WARN_ONCE: > > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 1177 at arch/m68k/kernel/ptrace.c:91 get_reg+0x90/0xb8 > Modules linked in: > CPU: 0 PID: 1177 Comm: strace Not tainted 5.13.0-rc1-atari-fpuemu-exitfix+ > #1146 > Stack from 014b7f04: > 014b7f04 00336401 00336401 000278f0 0032c015 0000005b 00000005 > 0002795a > 0032c015 0000005b 0000338c 00000009 00000000 00000000 ffffffe4 > 00000005 > 00000003 00000014 00000003 00000014 efc2b90c 0000338c 0032c015 > 0000005b > 00000009 00000000 efc2b908 00912540 efc2b908 000034cc 00912540 > 00000005 > 00000000 efc2b908 00000003 00912540 8000110c c010b0a4 efc2b90c > 0002d1d8 > 00912540 00000003 00000014 efc2b908 0000049a 00000014 efc2b908 > 800acaa8 > Call Trace: [<000278f0>] __warn+0x9e/0xb4 > [<0002795a>] warn_slowpath_fmt+0x54/0x62 > [<0000338c>] get_reg+0x90/0xb8 > [<0000338c>] get_reg+0x90/0xb8 > [<000034cc>] arch_ptrace+0x7e/0x250 > [<0002d1d8>] sys_ptrace+0x232/0x2f8 > [<00002ab6>] syscall+0x8/0xc > [<0000c00b>] lower+0x7/0x20 > > ---[ end trace ee4be53b94695793 ]--- > > Syscall numbers are actually 90 and 192 - sys_old_mmap and sys_mmap2 on > m68k. Used the calculator on my Ubuntu desktop, that appears to be a little > confused about hex to decimal conversions. > > I hope that makes more sense? Not really; what is the condition you are checking? The interesting trace is not that with get_reg() - it's that of the process being traced. You are not accessing the stack of caller of ptrace(2) here, so you want to know that SAVE_SWITCH_STACK had been done by the tracee, not tracer. And if that had been strace ls, you have TIF_SYSCALL_TRACE set for ls, so * ls hits system_call * notices TIF_SYSCALL_TRACE and goes to do_trace_entry * does SAVE_SWITCH_STACK there * calls syscall_trace(), which calls ptrace_notify() * ptrace_notify() calls ptrace_do_notify(), which calls ptrace_stop() * ptrace_stop() arranges for tracer to be woken up and gives CPU up, with TASK_TRACED as process state. That's the callchain in ls, and switch_stack accessed by get_reg() from strace is the one on ls(1) stack created by SAVE_SWITCH_STACK.
