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Biederman" , Wander Lairson Costa , Stafford Horne , Kefeng Wang , Oleg Nesterov , Andrew Morton , Thomas Gleixner , Sebastian Andrzej Siewior , Andy Lutomirski , "Liam R. Howlett" , Fenghua Yu , Andrei Vagin , linux-kernel@vger.kernel.org (open list) Cc: Paul McKenney Subject: [PATCH v2 1/4] sched/task: Add the put_task_struct_atomic_safe function Date: Fri, 20 Jan 2023 12:02:39 -0300 Message-Id: <20230120150246.20797-2-wander@redhat.com> In-Reply-To: <20230120150246.20797-1-wander@redhat.com> References: <20230120150246.20797-1-wander@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1755555214927726207?= X-GMAIL-MSGID: =?utf-8?q?1755555214927726207?= With PREEMPT_RT, it is unsafe to call put_task_struct() in atomic contexts because it indirectly acquires sleeping locks. Introduce put_task_struct_atomic_safe(), which schedules __put_task_struct() through call_rcu() when the kernel is compiled with PREEMPT_RT. A more natural approach would use a workqueue, but since in PREEMPT_RT we can't allocate dynamic memory from atomic context, the code would become more complex because we would need to put the work_struct instance in the task_struct and initialize it when we allocate a new task_struct. Signed-off-by: Wander Lairson Costa Cc: Paul McKenney Cc: Thomas Gleixner --- include/linux/sched/task.h | 21 +++++++++++++++++++++ kernel/fork.c | 8 ++++++++ 2 files changed, 29 insertions(+) diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index 357e0068497c..80b4c5812563 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -127,6 +127,27 @@ static inline void put_task_struct_many(struct task_struct *t, int nr) void put_task_struct_rcu_user(struct task_struct *task); +extern void __delayed_put_task_struct(struct rcu_head *rhp); + +static inline void put_task_struct_atomic_safe(struct task_struct *task) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + /* + * Decrement the refcount explicitly to avoid unnecessarily + * calling call_rcu. + */ + if (refcount_dec_and_test(&task->usage)) + /* + * under PREEMPT_RT, we can't call put_task_struct + * in atomic context because it will indirectly + * acquire sleeping locks. + */ + call_rcu(&task->rcu, __delayed_put_task_struct); + } else { + put_task_struct(task); + } +} + /* Free all architecture-specific resources held by a thread. */ void release_thread(struct task_struct *dead_task); diff --git a/kernel/fork.c b/kernel/fork.c index 9f7fe3541897..3d7a4e9311b3 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -859,6 +859,14 @@ void __put_task_struct(struct task_struct *tsk) } EXPORT_SYMBOL_GPL(__put_task_struct); +void __delayed_put_task_struct(struct rcu_head *rhp) +{ + struct task_struct *task = container_of(rhp, struct task_struct, rcu); + + __put_task_struct(task); +} +EXPORT_SYMBOL_GPL(__delayed_put_task_struct); + void __init __weak arch_task_cache_init(void) { } /*