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Thu, 02 Apr 2026 16:23:40 -0700 (PDT) Received: from localhost ([2601:645:8a00:6e44:c6ab:7340:c926:8c92]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2ca78df3b84sm3470455eec.5.2026.04.02.16.23.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Apr 2026 16:23:40 -0700 (PDT) From: Josh Snyder Date: Thu, 02 Apr 2026 16:23:38 -0700 Subject: [PATCH] tick/nohz: fix inverted return value in check_tick_dependency() fast path Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260402-fix-idle-tick2-v1-1-eecb589649d3@code406.com> X-B4-Tracking: v=1; b=H4sIAHn6zmkC/yWM3QpAQBBGX0VzbWtNfuJV5II1yyC0i5S8u8Hl+ frOucCTY/JQBBc4OtjzMgtEYQCmr+eOFLfCgBpTHWtUlk+ZJlIbmxFVouvY5mlrE8xApNWRPL5 gWf3s92Ygs70VuO8HGzWMVHIAAAA= X-Change-ID: 20260402-fix-idle-tick2-50a4f96df527 To: Anna-Maria Behnsen , Frederic Weisbecker , Ingo Molnar , Thomas Gleixner , "Ionut Nechita (Sunlight Linux)" Cc: linux-kernel@vger.kernel.org, Josh Snyder X-Mailer: b4 0.15.1 X-Developer-Signature: v=1; a=ed25519-sha256; t=1775172219; l=1375; i=josh@code406.com; s=20260402; h=from:subject:message-id; bh=xVUvvfZo4zokI5g3rlmrqBbt0gRsd0GvK5LpS5LUSNM=; b=TZmmVirIs9xlCI21rnYvg3hNbR43Rb5aqNG+9DJ6USjIdVjo+Zx7+hjeU00VlTGvDqKNZSIf1 gsmMjI8AXNTA2ljqA2lasTAtByNhZqB0bONGHe7ErmeV48WlARfQLAo X-Developer-Key: i=josh@code406.com; a=ed25519; pk=J60jemVD5rPt9HnGvw/AAQ6RPciMTW8aAgWykCCnCXg= Commit 56534673cea7f ("tick/nohz: Optimize check_tick_dependency() with early return") added a fast path that returns !val when the tick_stop tracepoint is disabled. This is inverted: the slow path returns true when a dependency IS found (val !=3D 0), but !val returns true when val is zero (no dependency). The result is that can_stop_full_tick() sees "dependency found" when there are none, and the tick never stops on nohz_full CPUs. Fix by returning val instead of !val, matching the slow-path semantics. Fixes: 56534673cea7f ("tick/nohz: Optimize check_tick_dependency() with ear= ly return") Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Josh Snyder --- kernel/time/tick-sched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index f7907fadd63f2..4324f3838ab0d 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -345,7 +345,7 @@ static bool check_tick_dependency(atomic_t *dep) int val =3D atomic_read(dep); =20 if (likely(!tracepoint_enabled(tick_stop))) - return !val; + return val; =20 if (val & TICK_DEP_MASK_POSIX_TIMER) { trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER); --- base-commit: 4f59dbcc2a99c8dd9b438c4e9ccb0e4870ef92f6 change-id: 20260402-fix-idle-tick2-50a4f96df527 Best regards, -- =20 Josh