From: "Paul E. McKenney" paulmck@kernel.org
[ Upstream commit 46faf9d8e1d52e4a91c382c6c72da6bd8e68297b ]
Holding a mutex across synchronize_rcu_tasks() and acquiring that same mutex in code called from do_exit() after its call to exit_tasks_rcu_start() but before its call to exit_tasks_rcu_stop() results in deadlock. This is by design, because tasks that are far enough into do_exit() are no longer present on the tasks list, making it a bit difficult for RCU Tasks to find them, let alone wait on them to do a voluntary context switch. However, such deadlocks are becoming more frequent. In addition, lockdep currently does not detect such deadlocks and they can be difficult to reproduce.
In addition, if a task voluntarily context switches during that time (for example, if it blocks acquiring a mutex), then this task is in an RCU Tasks quiescent state. And with some adjustments, RCU Tasks could just as well take advantage of that fact.
This commit therefore initializes the data structures that will be needed to rely on these quiescent states and to eliminate these deadlocks.
Link: https://lore.kernel.org/all/20240118021842.290665-1-chenzhongjin@huawei.com/
Reported-by: Chen Zhongjin chenzhongjin@huawei.com Reported-by: Yang Jihong yangjihong1@huawei.com Signed-off-by: Paul E. McKenney paulmck@kernel.org Tested-by: Yang Jihong yangjihong1@huawei.com Tested-by: Chen Zhongjin chenzhongjin@huawei.com Reviewed-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Boqun Feng boqun.feng@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- init/init_task.c | 1 + kernel/fork.c | 1 + kernel/rcu/tasks.h | 2 ++ 3 files changed, 4 insertions(+)
diff --git a/init/init_task.c b/init/init_task.c index 5727d42149c33..65f037bff457a 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -152,6 +152,7 @@ struct task_struct init_task .rcu_tasks_holdout = false, .rcu_tasks_holdout_list = LIST_HEAD_INIT(init_task.rcu_tasks_holdout_list), .rcu_tasks_idle_cpu = -1, + .rcu_tasks_exit_list = LIST_HEAD_INIT(init_task.rcu_tasks_exit_list), #endif #ifdef CONFIG_TASKS_TRACE_RCU .trc_reader_nesting = 0, diff --git a/kernel/fork.c b/kernel/fork.c index 10917c3e1f036..6bacd515e0eb5 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1981,6 +1981,7 @@ static inline void rcu_copy_process(struct task_struct *p) p->rcu_tasks_holdout = false; INIT_LIST_HEAD(&p->rcu_tasks_holdout_list); p->rcu_tasks_idle_cpu = -1; + INIT_LIST_HEAD(&p->rcu_tasks_exit_list); #endif /* #ifdef CONFIG_TASKS_RCU */ #ifdef CONFIG_TASKS_TRACE_RCU p->trc_reader_nesting = 0; diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 3580055342ca9..ac8eb667a6707 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -277,6 +277,8 @@ static void cblist_init_generic(struct rcu_tasks *rtp) rtpcp->rtpp = rtp; if (!rtpcp->rtp_blkd_tasks.next) INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks); + if (!rtpcp->rtp_exit_list.next) + INIT_LIST_HEAD(&rtpcp->rtp_exit_list); }
pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d.\n", rtp->name,