The first is something that has come up a few times and has been
worked out individually, but it's come up now enough that the problem
should be generic. Tracepoints are protected by RCU sched. There are
several tracepoints within core infrastructure like kfree().
If a tracepoint is called when the CPU is going down, or when it's
coming up but has yet to be recognized by RCU, a RCU warning is
triggered. This is a true bug as that tracepoint is not protected by
RCU. Usually, this is taken care of by testing for cpu online as
a tracepoint condition. But as this is happening more often, moving
it from a individual tracepoint to a check in the tracepoint infrastructure
is more robust.
Note, there is now a duplicate of a cpu online test, because this update
does not remove the individual checks. But the overhead is small enough
that the removal can be done in another release.
The second change is strange linker breakage due to the branch tracer's
builtin_constant_p() check failing, and treating the condition as a
variable instead of a constant. Arnd Bergmann found that this can be
fixed by testing !!(cond) instead of just (cond).
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Merge tag 'trace-fixes-v4.5-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing fixes from Steven Rostedt:
"This includes two fixes.
The first is something that has come up a few times and has been
worked out individually, but it's come up now enough that the problem
should be generic. Tracepoints are protected by RCU sched. There are
several tracepoints within core infrastructure like kfree(). If a
tracepoint is called when the CPU is going down, or when it's coming
up but has yet to be recognized by RCU, a RCU warning is triggered.
This is a true bug as that tracepoint is not protected by RCU.
Usually, this is taken care of by testing for cpu online as a
tracepoint condition. But as this is happening more often, moving it
from a individual tracepoint to a check in the tracepoint
infrastructure is more robust.
Note, there is now a duplicate of a cpu online test, because this
update does not remove the individual checks. But the overhead is
small enough that the removal can be done in another release.
The second change is strange linker breakage due to the branch
tracer's builtin_constant_p() check failing, and treating the
condition as a variable instead of a constant. Arnd Bergmann found
that this can be fixed by testing !!(cond) instead of just (cond)"
* tag 'trace-fixes-v4.5-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
tracing: Fix freak link error caused by branch tracer
tracepoints: Do not trace when cpu is offline
a9f70bd4e7