• Hannes Frederic Sowa's avatar
    static_key: WARN on usage before jump_label_init was called · c4b2c0c5
    Hannes Frederic Sowa authored
    Usage of the static key primitives to toggle a branch must not be used
    before jump_label_init() is called from init/main.c. jump_label_init
    reorganizes and wires up the jump_entries so usage before that could
    have unforeseen consequences.
    
    Following primitives are now checked for correct use:
    * static_key_slow_inc
    * static_key_slow_dec
    * static_key_slow_dec_deferred
    * jump_label_rate_limit
    
    The x86 architecture already checks this by testing if the default_nop
    was already replaced with an optimal nop or with a branch instruction. It
    will panic then. Other architectures don't check for this.
    
    Because we need to relax this check for the x86 arch to allow code to
    transition from default_nop to the enabled state and other architectures
    did not check for this at all this patch introduces checking on the
    static_key primitives in a non-arch dependent manner.
    
    All checked functions are considered slow-path so the additional check
    does no harm to performance.
    
    The warnings are best observed with earlyprintk.
    
    Based on a patch from Andi Kleen.
    
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Andi Kleen <andi@firstfloor.org>
    Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    c4b2c0c5
jump_label_ratelimit.h 921 Bytes