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    SubjectRe: Question: livepatch failed for new fork() task stack unreliable
    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

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