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srcu: Fix warning to permit SRCU-fast readers in NMI handlers

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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 <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Link: https://patch.msgid.link/8232efe8-a7a3-446c-af0b-19f9b523b4f7@paulmck-laptop
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Paul E. McKenney 2026-01-29 17:30:44 -08:00 • committed by Steven Rostedt (Google)
parent f7d327654b
commit a77cb6a867
1 changed files with 2 additions and 1 deletions
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3
kernel/rcu/srcutree.c
View file

@ -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);