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    SubjectRe: try_to_freeze() called with IRQs disabled on ARM
    On Fri, Sep 02, 2011 at 04:47:35PM +0200, Ulrich Weigand wrote:
    > Assume the scenario you initally describe, where a first signal is
    > ignored and leads to system call restart. With your latest patch,
    > you call into syscall_restart which sets everything up to restart
    > the call (with interrupts disabled).

    I don't think SIG_IGN signals even set the TIF work flag, so they
    never even cause a call into do_signal(). Therefore, as far as
    syscalls go, attempting to send a process (eg) a SIGINT which its
    handler is set to SIG_IGN results in the process not even being
    notified about the attempt - we won't even wake up while the
    syscall is sleeping.

    > To really fix this case would probably require some way for the
    > debugger to save and restore the restore_block saved state. This
    > is not quite trivial, since it would expose that state to user space,
    > effectively creating a new ABI (and probably requiring sanity checks
    > to ensure a valid state is restored). This probably cannot be fixed
    > by one architecture for itself, but would need support from common
    > kernel code.

    Such state would have to be crytographically signed or kept entirely
    within the kernel, as it would otherwise mean that you could redirect
    the kernel PC to anywhere...


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