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Thu, 06 Aug 2026 01:20:34 -0700 (PDT) Received: from mi-HP-ProDesk-600-G5-PCI-MT.mioffice.cn ([43.224.245.239]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d0a9ff6b34sm27660145ad.26.2026.08.06.01.20.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2026 01:20:34 -0700 (PDT) From: "Guanyou.Chen" X-Google-Original-From: "Guanyou.Chen" To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Andrew Morton Cc: Thomas Gleixner , Felix Moessbauer , Dietmar Eggemann , Steven Rostedt , Kees Cook , K Prateek Nayak , chenguanyou@xiaomi.com, linqiaoting@xiaomi.com, chunhui.li@mediatek.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] fork: fix default_timer_slack_ns inheritance from RT parent Date: Thu, 6 Aug 2026 16:20:09 +0800 Message-Id: <20260806082009.144846-1-chenguanyou@xiaomi.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Per prctl(2), "Timer slack is not applied to threads that are scheduled under a real-time scheduling policy." RT tasks' timer_slack_ns is forcibly 0 - not a user-chosen value but a "not applicable" state. When copy_process() sets the child's default_timer_slack_ns from the parent's timer_slack_ns, it inherits this forced 0 for RT parents. This corrupts the child's reset target, making prctl(PR_SET_TIMERSLACK, 0) and sched_setscheduler() back to NORMAL unable to restore a meaningful default. Fix this by using default_timer_slack_ns (which preserves the pre-RT value) when the parent is RT/DL. For non-RT parents, timer_slack_ns is a meaningful user value and the existing behavior is preserved. Fixes: ed4fb6d7ef68 ("hrtimer: Use and report correct timerslack values for= realtime tasks") Depends-on: 63c1a12bc0e0 ("sched: restore timer_slack_ns when resetting RT = policy on fork") Reported-by: Qiaoting.Lin Signed-off-by: Guanyou.Chen Signed-off-by: Chunhui.Li --- kernel/fork.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index 65113a304518..bc4df18bfd90 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include #include @@ -2133,7 +2134,10 @@ __latent_entropy struct task_struct *copy_process( retval =3D -EAGAIN; #endif =20 - p->default_timer_slack_ns =3D current->timer_slack_ns; + if (rt_or_dl_task_policy(current)) + p->default_timer_slack_ns =3D current->default_timer_slack_ns; + else + p->default_timer_slack_ns =3D current->timer_slack_ns; =20 #ifdef CONFIG_PSI p->psi_flags =3D 0; --=20 2.34.1