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Wed, 29 Apr 2026 06:32:00 -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 d9443c01a7336-2b98895dbcesm24166985ad.63.2026.04.29.06.31.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Apr 2026 06:32:00 -0700 (PDT) From: zhidao su X-Google-Original-From: zhidao su To: tj@kernel.org Cc: void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org, zhidao su Subject: [PATCH] sched_ext: Fix sched_ext_dead() race with scx_root_enable_workfn() Date: Wed, 29 Apr 2026 21:31:55 +0800 Message-ID: <20260429133155.3825247-1-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: quoted-printable Content-Type: text/plain; charset="utf-8" In CONFIG_EXT_SUB_SCHED, scx_task_sched(p) returns p->scx.sched instead of scx_root. scx_root_enable_workfn() initializes tasks in two steps: scx_init_task(sch, p, false) /* state=3DINIT, p->scx.sched still NULL */ scx_set_task_sched(p, sch) /* p->scx.sched =3D sch */ Between these two steps, a concurrent sched_ext_dead() can call scx_task_sched(p), get NULL, and pass it to scx_disable_and_exit_task() which crashes in SCX_HAS_OP(NULL, ...). In sched_ext_dead(), skip scx_disable_and_exit_task() when state=3DINIT and p->scx.sched is still NULL, and reset state to NONE. In scx_root_enable_workfn(), after scx_init_task() returns, skip scx_set_task_sched() if sched_ext_dead() has already removed @p from scx_tasks. Fixes: 073d4f0667b0 ("sched_ext: Refactor task init/exit helpers") Signed-off-by: zhidao su --- kernel/sched/ext.c | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index f7b1b16e81a5..1872af65b103 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -3887,9 +3887,21 @@ void sched_ext_dead(struct task_struct *p) struct rq_flags rf; struct rq *rq; =20 - rq =3D task_rq_lock(p, &rf); - scx_disable_and_exit_task(scx_task_sched(p), p); - task_rq_unlock(rq, p, &rf); + /* + * scx_root_enable_workfn() may be concurrently initializing @p. + * scx_init_task() sets state=3DINIT before scx_set_task_sched() + * sets p->scx.sched. If we race that window, p->scx.sched is + * still NULL; skip scx_disable_and_exit_task() and reset state + * to NONE so @p leaves SCX cleanly. + */ + if (scx_get_task_state(p) =3D=3D SCX_TASK_INIT && + !rcu_access_pointer(p->scx.sched)) { + scx_set_task_state(p, SCX_TASK_NONE); + } else { + rq =3D task_rq_lock(p, &rf); + scx_disable_and_exit_task(scx_task_sched(p), p); + task_rq_unlock(rq, p, &rf); + } } } =20 @@ -6937,6 +6949,17 @@ static void scx_root_enable_workfn(struct kthread_wo= rk *work) goto err_disable_unlock_all; } =20 + /* + * sched_ext_dead() may have already cleaned up @p while locks + * were dropped in scx_task_iter_unlock(); skip it. + */ + scoped_guard(raw_spinlock_irq, &scx_tasks_lock) { + if (list_empty(&p->scx.tasks_node)) { + put_task_struct(p); + continue; + } + } + scx_set_task_sched(p, sch); scx_set_task_state(p, SCX_TASK_READY); =20 --=20 2.43.0