On Fri, May 29, 2020 at 06:10:59PM +0800, Wang ShaoBo wrote:
> Stack unreliable error is reported by stack_trace_save_tsk_reliable() when
> trying
> to insmod a hot patch for module modification, this results in frequent
> failures
> sometimes. We found this 'unreliable' stack is from task just fork.
For livepatch, this shouldn't actually be a failure. The patch will
just stay in the transition state until after the fork has completed.
Which should happen in a reasonable amount of time, right?
> 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();
Yes, this seems to be true for forked-but-not-yet-scheduled tasks.
I can look at fixing that. I have some ORC cleanups in progress which
are related to UNWIND_HINT_EMPTY and the end of the stack. I can add
this issue to the list of improvements.
> 2) The task has been scheduled but UNWIND_HINT_REGS not finished, at this time
> arch_stack_walk_reliable() terminates it's backtracing loop for pt_regs
> unknown
> and return -EINVAL because it's a user task.
Hm, do you see this problem with upstream? It seems like it should
work. arch_stack_walk_reliable() has this:
/* Success path for user tasks */
if (user_mode(regs))
return 0;
Where exactly is the error coming from?
--
Josh
