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Tue, 06 Oct 2026 19:29:22 -0700 (PDT) Received: from kernel.tail6741c6.ts.net ([216.195.201.24]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a89b5c5d9asm2090836a91.11.2026.10.06.19.29.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Oct 2026 19:29:22 -0700 (PDT) From: Kunwu Chan To: arnd@arndb.de, anna-maria@linutronix.de, frederic@kernel.org, mingo@kernel.org, tglx@kernel.org Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Kunwu Chan Subject: [PATCH v3 2/2] timers/nohz: Mark got_idle_tick accesses as same-CPU races Date: Wed, 7 Oct 2026 10:28:59 +0800 Message-ID: <20261007022859.60101-3-kunwu.chan@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261007022859.60101-1-kunwu.chan@gmail.com> References: <20261007022859.60101-1-kunwu.chan@gmail.com> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit got_idle_tick is a per-CPU flag set by the tick interrupt handler in tick_sched_do_timer() and read and cleared by the idle path in tick_nohz_idle_got_tick(). The flag is intentionally accessed without ordering or locking; a concurrent set can be overwritten by the clear. Use WRITE_ONCE_THIS_CPU() and READ_ONCE_THIS_CPU() to identify these as intentional races between execution contexts on the same CPU, rather than accesses that may race across CPUs. Suggested-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Signed-off-by: Kunwu Chan --- kernel/time/tick-sched.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 6c3fea386..a136bb247 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -269,7 +269,7 @@ static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now) } if (tick_sched_flag_test(ts, TS_FLAG_INIDLE)) - ts->got_idle_tick = 1; + WRITE_ONCE_THIS_CPU(ts->got_idle_tick, 1); } static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) @@ -1248,8 +1248,8 @@ bool tick_nohz_idle_got_tick(void) { struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); - if (ts->got_idle_tick) { - ts->got_idle_tick = 0; + if (READ_ONCE_THIS_CPU(ts->got_idle_tick)) { + WRITE_ONCE_THIS_CPU(ts->got_idle_tick, 0); return true; } return false; -- 2.43.0