On Thu, Jan 29, 2026 at 05:30:44PM -0800, Paul E. McKenney wrote: > srcu: Fix warning to permit SRCU-fast readers in NMI handlers >
This line seems to be duplicated ;) > SRCU-fast is designed to be used in NMI handlers, even going so far > as to use atomic operations for architectures supporting NMIs but not > providing NMI-safe per-CPU atomic operations. However, the WARN_ON_ONCE() > in __srcu_check_read_flavor() complains if SRCU-fast is used in an NMI > handler. This commit therefore modifies that WARN_ON_ONCE() to avoid > such complaints. > > Reported-by: Steven Rostedt <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > Tested-by: Steven Rostedt <[email protected]> > Cc: Andrii Nakryiko <[email protected]> > Cc: Alexei Starovoitov <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: [email protected] > I queued it with the duplicate line removed, please see below. Regards, Boqun ---------------------->8 Subject: [PATCH] srcu: Fix warning to permit SRCU-fast readers in NMI handlers SRCU-fast is designed to be used in NMI handlers, even going so far as to use atomic operations for architectures supporting NMIs but not providing NMI-safe per-CPU atomic operations. However, the WARN_ON_ONCE() in __srcu_check_read_flavor() complains if SRCU-fast is used in an NMI handler. This commit therefore modifies that WARN_ON_ONCE() to avoid such complaints. [boqun: Remove the duplicate title line] Reported-by: Steven Rostedt <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> Tested-by: Steven Rostedt <[email protected]> Cc: Andrii Nakryiko <[email protected]> Cc: Alexei Starovoitov <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: [email protected] Signed-off-by: Boqun Feng <[email protected]> --- kernel/rcu/srcutree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index c469c708fdd6..66ba6a2f83d3 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -789,7 +789,8 @@ void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) struct srcu_data *sdp; /* NMI-unsafe use in NMI is a bad sign, as is multi-bit read_flavor values. */ - WARN_ON_ONCE((read_flavor != SRCU_READ_FLAVOR_NMI) && in_nmi()); + WARN_ON_ONCE(read_flavor != SRCU_READ_FLAVOR_NMI && + read_flavor != SRCU_READ_FLAVOR_FAST && in_nmi()); WARN_ON_ONCE(read_flavor & (read_flavor - 1)); sdp = raw_cpu_ptr(ssp->sda); --
