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    SubjectRe: [PATCH] signals: check_kill_permission: don't check creds if same_thread_group()
    On 05/18, David Howells wrote:
    >
    > Oleg Nesterov <oleg@redhat.com> wrote:
    >
    > > Yes, but both current_cred() and same_thread_group(current, t) call
    > > get_current(), and gcc doesn't cache the result because we call
    > > audit_signal_info() in between.
    >
    > Sorry, yes. I was reading get_current() as current_cred() for some reason.
    >
    > However, you are _still_ calling get_current() twice... So that bit of your
    > changelog isn't really correct.

    If I read kernel/signal.s correctly - no.

    Well, yes, get_current() is still called twice inside check_kill_permission().
    But this is because we have audit_signal_info()->audit_dummy_context() which
    uses current too.

    But "cred = current_cred()" and same_thread_group(current, t) read
    gs:current_task only once, so this change really helps (although the
    optimization is very minor, of course).

    > In fact, get_current() should be __attribute_const__ since it can't change
    > whilst you're looking at it, except within switch_to(), probably in a piece of
    > assembly code, so gcc should be free to cache it as long as it likes.

    Agreed! I thought about this many times.

    Oleg.



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