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Mon, 09 Mar 2026 09:30:32 -0700 (PDT) Received: from eric-wcnlab.tail151456.ts.net ([2001:288:7001:1099:3cea:adff:13a5:9a2c]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-359bc9d4392sm5687519a91.4.2026.03.09.09.30.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Mar 2026 09:30:32 -0700 (PDT) From: Cheng-Yang Chou To: sched-ext@lists.linux.dev Cc: tj@kernel.org, void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, jserv@ccns.ncku.edu.tw, yphbchou0911@gmail.com Subject: [PATCH 0/1] sched_ext: Fix deadlock in scx_claim_exit() by deferring descendant propagation Date: Tue, 10 Mar 2026 00:30:24 +0800 Message-ID: <20260309163025.2240221-1-yphbchou0911@gmail.com> X-Mailer: git-send-email 2.48.1 Precedence: bulk X-Mailing-List: sched-ext@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit While testing scx_rustland under vng, the locking dependency checker reported a circular locking dependency: [ 31.801757] ====================================================== [ 31.801786] WARNING: possible circular locking dependency detected [ 31.801812] 7.0.0-rc2+ #31 Tainted: G E [ 31.801835] ------------------------------------------------------ [ 31.801860] swapper/7/0 is trying to acquire lock: [ 31.801884] ffffffffa4ac1638 (scx_sched_lock){-...}-{2:2}, at: scx_claim_exit+0x7a/0x180 [ 31.801923] [ 31.801923] but task is already holding lock: [ 31.801951] ffff8ce0bcbc5ca0 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x28/0xc0 [ 31.801990] [ 31.801990] which lock already depends on the new lock. [ 31.801990] [ 31.802021] [ 31.802021] the existing dependency chain (in reverse order) is: [ 31.802050] [ 31.802050] -> #1 (&rq->__lock){-.-.}-{2:2}: [ 31.802079] _raw_spin_lock_nested+0x2d/0x50 [ 31.802103] raw_spin_rq_lock_nested+0x28/0xc0 [ 31.802128] scx_bypass+0x14e/0x4e0 [ 31.802147] scx_root_enable_workfn+0x2ce/0xa10 [ 31.802171] kthread_worker_fn+0xbf/0x3c0 [ 31.802199] kthread+0x109/0x140 [ 31.802218] ret_from_fork+0x3fd/0x490 [ 31.802242] ret_from_fork_asm+0x1a/0x30 [ 31.802267] [ 31.802267] -> #0 (scx_sched_lock){-...}-{2:2}: [ 31.802296] __lock_acquire+0x172e/0x2830 [ 31.802320] lock_acquire+0xd5/0x330 [ 31.802339] _raw_spin_lock_irqsave+0x49/0x80 [ 31.802363] scx_claim_exit+0x7a/0x180 [ 31.802387] scx_vexit+0x3a/0xd0 [ 31.802406] scx_exit+0x50/0x80 [ 31.802425] scx_tick+0x114/0x120 [ 31.802445] sched_tick+0x12e/0x3a0 [ 31.802464] update_process_times+0x90/0xf0 [ 31.802488] tick_nohz_handler+0x97/0x1b0 [ 31.802512] __hrtimer_run_queues+0xac/0x3a0 [ 31.802539] hrtimer_interrupt+0x116/0x280 [ 31.802564] __sysvec_apic_timer_interrupt+0x6b/0x1e0 [ 31.802589] sysvec_apic_timer_interrupt+0x9b/0xc0 [ 31.802613] asm_sysvec_apic_timer_interrupt+0x1b/0x20 [ 31.802642] pv_native_safe_halt+0xb/0x10 [ 31.802669] arch_cpu_idle+0x9/0x10 [ 31.802687] default_idle_call+0x7c/0x220 [ 31.802713] do_idle+0x211/0x260 [ 31.802732] cpu_startup_entry+0x29/0x30 [ 31.802756] start_secondary+0x12d/0x170 [ 31.802780] common_startup_64+0x13e/0x141 [ 31.802804] [ 31.802804] other info that might help us debug this: [ 31.802804] [ 31.802834] Possible unsafe locking scenario: [ 31.802834] [ 31.802859] CPU0 CPU1 [ 31.802879] ---- ---- [ 31.802899] lock(&rq->__lock); [ 31.802918] lock(scx_sched_lock); [ 31.802949] lock(&rq->__lock); [ 31.802978] lock(scx_sched_lock); [ 31.802997] [ 31.802997] *** DEADLOCK *** Link to full log: https://gist.github.com/EricccTaiwan/bc7d8eac7a9a31af36a2e9f0a295da7c Thanks, Cheng-Yang --- Cheng-Yang Chou (1): sched_ext: Fix deadlock in scx_claim_exit() by deferring descendant propagation kernel/sched/ext.c | 43 ++++++++++++++++++++++++++----------------- 1 file changed, 26 insertions(+), 17 deletions(-) -- 2.48.1