[uml-devel] How to go about debugging fork in -skas0?

[uml-devel] How to go about debugging fork in -skas0?

[Rob Landley]

As I mentioned on the -user list, when I build 2.6.15-rc1 or -rc2 on my x86 
laptop, it works just fine as long as PID 1 never forks.  As soon as fork() 
gets called, I get the attached panic.

I'm not sure how to go about debugging this.  Is it the clone stub handler 
again, do you think?  This is an area where I don't particularly understand 
how it worked in the first place.  I can go stare at 2.6.14 (which works) and 
try to work out what changed...

Rob

EIP: 0073:[<ffffe410>] CPU: 0 Not tainted ESP: 007b:bfad8780 EFLAGS: 00200206
    Not tainted
EAX: ffffffda EBX: 01200011 ECX: 00000000 EDX: 00000000
ESI: 00000000 EDI: 401922e8 EBP: bfad87d8 DS: 007b ES: 007b
088a787c:  [<08080b7d>] notifier_call_chain+0x2d/0x50
088a7898:  [<08071411>] panic+0x71/0x110
088a78b0:  [<0805e8f0>] wait_stub_done+0x100/0x190
088a791c:  [<0806bc25>] ptrace_setregs+0x25/0x40
088a7930:  [<0805f320>] copy_context_skas0+0x1b0/0x270
088a7a0c:  [<0805e68a>] init_new_context_skas+0x11a/0x1a0
088a7a3c:  [<0806f872>] copy_mm+0xd2/0x380
088a7a80:  [<08070455>] copy_process+0x415/0xda0
088a7aa0:  [<0805dcb3>] setjmp_wrapper+0x83/0x90
088a7ac4:  [<0805dc67>] setjmp_wrapper+0x37/0x90
088a7ae4:  [<0805a745>] change_signals+0x65/0x90
088a7b60:  [<08070e4f>] do_fork+0x6f/0x1cc
088a7b80:  [<0807f5b4>] kernel_sigprocmask+0x64/0x140
088a7b90:  [<08060ae6>] copy_to_user_skas+0x86/0xa0
088a7ba0:  [<08060a20>] copy_chunk_to_user+0x0/0x40
088a7bc8:  [<0806ce89>] sys_clone+0x79/0xa0
088a7bf4:  [<080601dc>] handle_syscall+0xec/0x100
088a7c64:  [<0805eaa8>] handle_trap+0x28/0x130
088a7c8c:  [<0805f114>] userspace+0x1c4/0x220
088a7cd8:  [<08055f50>] init+0x0/0x170
088a7ce4:  [<0805fbf2>] new_thread_handler+0xf2/0x130


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