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[87.205.15.91]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48db9acee65sm3650230f8f.49.2026.10.09.05.33.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Oct 2026 05:33:13 -0700 (PDT) From: Krystian Kaniewski To: Vinicius Costa Gomes , Jamal Hadi Salim , Jiri Pirko , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , Vladimir Oltean , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net v2 0/2] net/sched: taprio: fix RCU stall from replayed schedule entries Date: Fri, 9 Oct 2026 14:33:07 +0200 Message-ID: <20261009123309.284193-1-krystianmkaniewski@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit syzbot reported an RCU stall with a software taprio schedule made of a single 127 ns entry. When advance_sched() falls behind, it replays every missed entry inside the timer interrupt and the backlog only grows. Patch 2 makes it continue from the entry in progress instead. Patch 2 then checks for an admin schedule handover once after catching up. That requires the cycle_time_extension comparison to be monotonic, so the sum now saturates instead of wrapping. As a result a large extension can hand over to an admin schedule whose start time leaves no room for the timestamps derived from it. Initializing such a schedule already overflows today, and a carefully chosen extension can already reach it. Patch 1 rejects these schedules at configuration time and comes first, so the series never hands over to one. v2: - patch 2: do not use the list iterator after the loop in taprio_entry_at(). The helper returns the entry through a separate pointer that is set inside the loop (Jakub) - patch 2: wrap the lines longer than 80 columns - patch 1: no change v1: https://lore.kernel.org/all/20261006113335.241564-1-krystianmkaniewski@gmail.com/ Krystian Kaniewski (2): net/sched: taprio: reject software schedules that overflow their timestamps net/sched: taprio: do not replay missed entries in advance_sched() net/sched/sch_taprio.c | 179 ++++++++++++++++++++++++++++++++++++----- 1 file changed, 157 insertions(+), 22 deletions(-) base-commit: af39eb111ce6b5eba9c08513b62c4868eb7e7fd5 -- 2.53.0