Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 1/3] srcu: Warn when NMI-unsafe API is used in NMI | Date | Thu, 13 Oct 2022 19:22:42 +0200 |
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Using the NMI-unsafe reader API from within NMIs is very likely to be buggy for three reasons:
1) NMIs aren't strictly re-entrant (a pending nested NMI will execute at the end of the current one) so it should be fine to use a non-atomic increment here. However breakpoints can still interrupt NMIs and if a breakpoint callback has a reader on that same ssp, a racy increment can happen.
2) If the only reader site for a given ssp is in an NMI, RCU is definetly a better choice over SRCU.
3) Because of the previous reason (2), an ssp having an SRCU read side critical section in an NMI is likely to have another one from a task context.
For all these reasons, warn if an nmi unsafe reader API is used from an NMI.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org> --- kernel/rcu/srcutree.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index c54142374793..8b7ef1031d89 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -642,6 +642,8 @@ static void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe) if (!IS_ENABLED(CONFIG_PROVE_RCU)) return; + /* NMI-unsafe use in NMI is a bad sign */ + WARN_ON_ONCE(!nmi_safe && in_nmi()); sdp = raw_cpu_ptr(ssp->sda); old_nmi_safe_mask = READ_ONCE(sdp->srcu_nmi_safety); if (!old_nmi_safe_mask) { -- 2.25.1
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