static_key: WARN on usage before jump_label_init was called
authorHannes Frederic Sowa <hannes@stressinduktion.org>
Sat, 19 Oct 2013 19:48:53 +0000 (21:48 +0200)
committerDavid S. Miller <davem@davemloft.net>
Sat, 19 Oct 2013 23:45:35 +0000 (19:45 -0400)
commitc4b2c0c5f647aa1093e8f9097a30c17ce0f94d4d
tree37d56a25f147e626b68532543c8569a739f7fee3
parentb50026b5ac8fe2932e6af0c54b21da0913c4c1c7
static_key: WARN on usage before jump_label_init was called

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: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
include/linux/jump_label.h
include/linux/jump_label_ratelimit.h
init/main.c
kernel/jump_label.c