On Sat, May 30, 2020 at 10:21:19AM +0800, Wangshaobo (bobo) wrote: > 1) when a user mode task just fork start excuting ret_from_fork() till > schedule_tail, unwind_next_frame found > > orc->sp_reg is ORC_REG_UNDEFINED but orc->end not equals zero, this time > arch_stack_walk_reliable() > > terminates it's backtracing loop for unwind_done() return true. then 'if > (!(task->flags & (PF_KTHREAD | PF_IDLE)))' > > in arch_stack_walk_reliable() true and return -EINVAL after. > > * The stack trace looks like that: > > ret_from_fork > > -=> UNWIND_HINT_EMPTY > > -=> schedule_tail /* schedule out */ > > ... > > -=> UNWIND_HINT_REGS /* UNDO */
Yes, makes sense. > 2) when using call_usermodehelper_exec_async() to create a user mode task, > ret_from_fork() still not exec whereas > > the task has been scheduled in __schedule(), at this time, orc->sp_reg is > ORC_REG_UNDEFINED but orc->end equals zero, > > unwind_error() return true and also terminates arch_stack_walk_reliable()'s > backtracing loop, end up return from > > 'if (unwind_error())' branch. > > * The stack trace looks like that: > > -=> call_usermodehelper_exec > > -=> do_exec > > -=> search_binary_handler > > -=> load_elf_binary > > -=> elf_map > > -=> vm_mmap_pgoff > > -=> down_write_killable > > -=> _cond_resched > > -=> __schedule /* scheduled to work */ > > -=> ret_from_fork /* UNDO */ I don't quite follow the stacktrace, but it sounds like the issue is the same as the first one you originally reported: > 1) The task was not actually scheduled to excute, at this time > UNWIND_HINT_EMPTY in ret_from_fork() has not reset unwind_hint, it's > sp_reg and end field remain default value and end up throwing an error > in unwind_next_frame() when called by arch_stack_walk_reliable(); Or am I misunderstanding? And to reiterate, these are not "livepatch failures", right? Livepatch doesn't fail when stack_trace_save_tsk_reliable() returns an error. It recovers gracefully and tries again later. -- Josh
