- The first one is a side effect caused by using SRCU for rcuidle
tracepoints. It seems that the perf was depending on the rcuidle
tracepoints to make RCU watch when it wasn't. The real fix will
bet to have perf use SRCU instead of depending on RCU watching,
but that can't be done until SRCU is safe to use in NMI context
(Paul's working on that).
- The second bug fix is for a bug that's been periodically making
my tests fail randomly for some time. I haven't had time to track
it down, but finally have. It has to do with stressing NMIs (via perf)
while enabling or disabling ftrace function handling with lockdep
enabled. If an interrupt happens and just as it returns, it sets
lockdep back to "interrupts enabled" but before it returns an NMI
is triggered, and if this happens while printk_nmi_enter has a
breakpoint attached to it (because ftrace is converting it to or from
nop to call fentry), the breakpoint trap also calls into lockdep,
and since returning from the NMI to a interrupt handler, interrupts
were disabled when the NMI went off, lockdep keeps its state as
interrupts disabled when it returns back from the interrupt handler
where interrupts are enabled. This causes lockdep_assert_irqs_enabled()
to trigger a false positive.
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Merge tag 'trace-v4.19-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing fixes from Steven Rostedt:
"This fixes two annoying bugs:
- The first one is a side effect caused by using SRCU for rcuidle
tracepoints. It seems that the perf was depending on the rcuidle
tracepoints to make RCU watch when it wasn't.
The real fix will be to have perf use SRCU instead of depending on
RCU watching, but that can't be done until SRCU is safe to use in
NMI context (Paul's working on that).
- The second bug fix is for a bug that's been periodically making my
tests fail randomly for some time. I haven't had time to track it
down, but finally have. It has to do with stressing NMIs (via perf)
while enabling or disabling ftrace function handling with lockdep
enabled.
If an interrupt happens and just as it returns, it sets lockdep
back to "interrupts enabled" but before it returns an NMI is
triggered, and if this happens while printk_nmi_enter has a
breakpoint attached to it (because ftrace is converting it to or
from nop to call fentry), the breakpoint trap also calls into
lockdep, and since returning from the NMI to a interrupt handler,
interrupts were disabled when the NMI went off, lockdep keeps its
state as interrupts disabled when it returns back from the
interrupt handler where interrupts are enabled.
This causes lockdep_assert_irqs_enabled() to trigger a false
positive"
* tag 'trace-v4.19-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
printk/tracing: Do not trace printk_nmi_enter()
tracing: Add back in rcu_irq_enter/exit_irqson() for rcuidle tracepoints
be65e2595b