Messages in this thread | | | Date | Tue, 18 May 2010 16:08:40 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] signals: check_kill_permission: don't check creds if same_thread_group() |
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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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