From 622996bf8475bf1d06cbb523dacc7469e7b9c864 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 25 Jun 2011 09:21:04 +0200 Subject: [PATCH 169/323] sched: Add saved_state for tasks blocked on sleeping locks Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz Spinlocks are state preserving in !RT. RT changes the state when a task gets blocked on a lock. So we need to remember the state before the lock contention. If a regular wakeup (not a RTmutex related wakeup) happens, the saved_state is updated to running. When the lock sleep is done, the saved state is restored. Signed-off-by: Thomas Gleixner --- include/linux/sched.h | 3 +++ kernel/sched/core.c | 34 ++++++++++++++++++++++++++++++++-- kernel/sched/sched.h | 1 + 3 files changed, 36 insertions(+), 2 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index d31da4867bb2..73defe42fd23 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -659,6 +659,8 @@ struct task_struct { #endif /* -1 unrunnable, 0 runnable, >0 stopped: */ volatile long state; + /* saved state for "spinlock sleepers" */ + volatile long saved_state; /* * This begins the randomizable portion of task_struct. Only @@ -1782,6 +1784,7 @@ extern struct task_struct *find_get_task_by_vpid(pid_t nr); extern int wake_up_state(struct task_struct *tsk, unsigned int state); extern int wake_up_process(struct task_struct *tsk); +extern int wake_up_lock_sleeper(struct task_struct *tsk); extern void wake_up_new_task(struct task_struct *tsk); #ifdef CONFIG_SMP diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 390b51366f5e..f6d40256c0d4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3305,7 +3305,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) int cpu, success = 0; preempt_disable(); - if (p == current) { + if (!IS_ENABLED(CONFIG_PREEMPT_RT) && p == current) { /* * We're waking current, this means 'p->on_rq' and 'task_cpu(p) * == smp_processor_id()'. Together this means we can special @@ -3335,8 +3335,26 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) */ raw_spin_lock_irqsave(&p->pi_lock, flags); smp_mb__after_spinlock(); - if (!(p->state & state)) + if (!(p->state & state)) { + /* + * The task might be running due to a spinlock sleeper + * wakeup. Check the saved state and set it to running + * if the wakeup condition is true. + */ + if (!(wake_flags & WF_LOCK_SLEEPER)) { + if (p->saved_state & state) { + p->saved_state = TASK_RUNNING; + success = 1; + } + } goto unlock; + } + /* + * If this is a regular wakeup, then we can unconditionally + * clear the saved state of a "lock sleeper". + */ + if (!(wake_flags & WF_LOCK_SLEEPER)) + p->saved_state = TASK_RUNNING; trace_sched_waking(p); @@ -3525,6 +3543,18 @@ int wake_up_process(struct task_struct *p) } EXPORT_SYMBOL(wake_up_process); +/** + * wake_up_lock_sleeper - Wake up a specific process blocked on a "sleeping lock" + * @p: The process to be woken up. + * + * Same as wake_up_process() above, but wake_flags=WF_LOCK_SLEEPER to indicate + * the nature of the wakeup. + */ +int wake_up_lock_sleeper(struct task_struct *p) +{ + return try_to_wake_up(p, TASK_UNINTERRUPTIBLE, WF_LOCK_SLEEPER); +} + int wake_up_state(struct task_struct *p, unsigned int state) { return try_to_wake_up(p, state, 0); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index c26b1c7009f4..d4bfc51358d3 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1753,6 +1753,7 @@ static inline int task_on_rq_migrating(struct task_struct *p) #define WF_FORK 0x02 /* Child wakeup after fork */ #define WF_MIGRATED 0x04 /* Internal use, task got migrated */ #define WF_ON_CPU 0x08 /* Wakee is on_cpu */ +#define WF_LOCK_SLEEPER 0x10 /* Wakeup spinlock "sleeper" */ /* * To aid in avoiding the subversion of "niceness" due to uneven distribution -- 2.43.0