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    SubjectRe: [BUG] ptraced process waiting on syscall may return kernel internal errnos
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    On Thu, 2007-06-14 at 16:58 +0400, Oleg Nesterov wrote:
    >
    > > Well, the only code path in which we'd want to call cancel_freezing() for kernel
    > > threads is when the freezing of kernel threads. However, this only happens if
    > > one of the kernel threads declares itself as freezable and the fails to call
    > > try_to_freeze(), which is a bug.
    >
    > But this happens? We know a lot of reasons why try_to_freeze() can fail just
    > because some kthread waits for already frozen task.

    The freezer is a deadlock-o-matic by design. It's one of the major if
    not the main reason why we don't use the code in kernel/power.c on
    PowerBooks for suspend-to-ram. I don't like it and paulus hates it.

    > Well, we can have very subtle problems because a kernel thread may run with
    > TIF_SIGPENDING forever. This means in particualar that any wait_event_interruptible()
    > can't succeed. I think this is worse than explicit failure (like -ERESSTART... leak),
    > because it is hard to reproduce/debug.

    Then just don't send signals to them...

    > > Moreover, I'm not sure that it's a good idea at all to send signals to kernel
    > > threads from the freezer, since in fact we only need to wake them up to make
    > > them call try_to_freeze() (after we've set TIF_FREEZE for them).
    >
    > Yes! I completely agree.

    Sounds like a plan...

    Freezer problem 1/102893264 solved.

    Ben.


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