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    SubjectRe: [PATCH] x86: kill handle_signal()->set_fs()
    On 07/10/2011 09:44 AM, Oleg Nesterov wrote:
    > handle_signal()->set_fs() has a nice comment which explains what
    > set_fs() is, but it doesn't explain why it is needed and why it
    > depends on CONFIG_X86_64.
    >
    > Afaics, the history of this confusion is:
    >
    > 1. I guess today nobody can explain why it was needed
    > in arch/i386/kernel/signal.c, perhaps it was always
    > wrong. This predates 2.4.0 kernel.
    >
    > 2. then it was copy-and-past'ed to the new x86_64 arch.
    >
    > 3. then it was removed from i386 (but not from x86_64)
    > by b93b6ca3 "i386: remove unnecessary code".
    >
    > 4. then it was reintroduced under CONFIG_X86_64 when x86
    > unified i386 and x86_64, because the patch above didn't
    > touch x86_64.
    >
    > Remove it. ->addr_limit should be correct. Even if it was possible
    > that it is wrong, it is too late to fix it after setup_rt_frame().
    >

    The main reason I could think of why this would be necessary is if we
    take an event while we have fs == KERNEL_DS inside the kernel which is
    then promoted to a signal. Are you absolutely sure that can't happen?

    In particular, there should be a setting upstream of this, as you're
    correctly pointing out that it's too late. If not, we might actually
    have a problem.

    -hpa


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