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Thu, 26 Mar 2026 13:42:44 -0700 (PDT) Received: from mi-HP-ProDesk-680-G6-PCI-Microtower-PC.mioffice.cn ([43.224.245.226]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b0cbfd17d9sm4004905ad.25.2026.03.26.13.42.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2026 13:42:44 -0700 (PDT) From: zhidao su X-Google-Original-From: zhidao su To: sched-ext@lists.linux.dev Cc: linux-kernel@vger.kernel.org, tj@kernel.org, void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, peterz@infradead.org, mingo@redhat.com, zhidao su Subject: [PATCH 0/4] sched_ext: fix three unreliable selftests and compat kfunc signature Date: Fri, 27 Mar 2026 04:42:34 +0800 Message-ID: <20260326204238.3755737-1-suzhidao@xiaomi.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Three selftests added in c50dcf533149 ("selftests/sched_ext: Add tests for SCX_ENQ_IMMED and scx_bpf_dsq_reenq()") have design flaws that prevent them from reliably triggering the kernel behavior they were written to verify. This series fixes all three, plus a related compat.bpf.h signature bug. - Patch 1: compat.bpf.h declares scx_bpf_dsq_reenq___compat with an explicit aux__prog parameter, but scx_bpf_dsq_reenq() is a KF_IMPLICIT_ARGS kfunc, so the BPF-side declaration must NOT include the implicit parameter. - Patch 2 (enq_immed): when the IMMED slow path fires, reenqueued tasks were re-inserted into CPU 0's local DSQ, immediately re-triggering the slow path and creating an infinite cycle that hits SCX_REENQ_LOCAL_MAX_REPEAT (256). Fix: redirect reenqueued tasks to SCX_DSQ_GLOBAL. - Patch 3 (dsq_reenq): dispatch consumed USER_DSQ directly, racing with the 5 ms BPF timer. By the time the timer fired, USER_DSQ was empty and scx_bpf_dsq_reenq() found nothing to reenqueue. Fix: two-DSQ design where USER_DSQ is never touched by dispatch. - Patch 4 (consume_immed): workers were spread across all CPUs, so USER_DSQ usually had only one task and dsq->nr never exceeded 1. Fix: pin all workers to CPU 0 via CPU affinity so USER_DSQ always has backlog; add dispatch loop to accumulate 2+ tasks and reliably trigger the IMMED slow path. All three tests verified with virtme-ng (PASSED: 30, FAILED: 0 across the full sched_ext selftest suite). zhidao su (4): tools/sched_ext: compat.bpf.h: fix scx_bpf_dsq_reenq___compat signature selftests/sched_ext: enq_immed: fix IMMED reenqueue livelock selftests/sched_ext: dsq_reenq: fix reliability with two-DSQ design selftests/sched_ext: consume_immed: fix reliability with CPU affinity tools/sched_ext/include/scx/compat.bpf.h | 4 +- .../selftests/sched_ext/consume_immed.bpf.c | 19 ++++++-- .../selftests/sched_ext/consume_immed.c | 15 +++++-- .../selftests/sched_ext/dsq_reenq.bpf.c | 45 ++++++++++++++----- .../selftests/sched_ext/enq_immed.bpf.c | 10 ++++- 5 files changed, 73 insertions(+), 20 deletions(-) -- 2.43.0