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authorFrederic Weisbecker <frederic@kernel.org>2022-10-13 19:22:42 +0200
committerPaul E. McKenney <paulmck@kernel.org>2022-10-21 10:15:53 -0700
commit6b77bb9b99c66c6596c58e7a25169bc2ea6b82dd (patch)
treec8e0c6a1fa368ea90142e40a7698f2e76fc86d3e
parent85bf37855ce287fe045a539441c0a3cd9c8b16fc (diff)
srcu: Warn when NMI-unsafe API is used in NMI
Using the NMI-unsafe reader API from within an NMI handler 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 srcu_struct structure is in an NMI handler, then RCU should be used instead of SRCU. 3) Because of the previous reason (2), an srcu_struct structure having an SRCU read side critical section in an NMI handler 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 handler. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
-rw-r--r--kernel/rcu/srcutree.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 87ae6f5c1eda..18bb696cff8c 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) {