diff options
| author | Frederic Weisbecker <frederic@kernel.org> | 2022-10-13 19:22:42 +0200 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-10-21 10:15:53 -0700 |
| commit | 6b77bb9b99c66c6596c58e7a25169bc2ea6b82dd (patch) | |
| tree | c8e0c6a1fa368ea90142e40a7698f2e76fc86d3e | |
| parent | 85bf37855ce287fe045a539441c0a3cd9c8b16fc (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.c | 2 |
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) { |