Messages in this thread Patch in this message | | | Date | Thu, 2 Mar 2023 16:56:13 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] pstore: Revert pmsg_lock back to a normal mutex |
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On Thu, 2 Mar 2023 16:36:03 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:
> I just noticed there's an rcu_read_lock() here around the loop. > I'm guessing that's to keep this race from happening. > Would have been nice to have a comment there stating such.
Knowing that rcu_read_lock() keeps the tasks safe, I made the optimization to only grab the spinlock (and disable interrupts) once, or whenever the top waiter changes.
-- Steve
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 010cf4e6d0b8..37820331857b 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1399,8 +1399,12 @@ static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter, struct task_struct *owner) { + struct rt_mutex_waiter *top_waiter; + struct rt_mutex_waiter *last_waiter = NULL; + struct task_struct *top_task = NULL; bool res = true; + /* rcu_read_lock keeps task_structs around */ rcu_read_lock(); for (;;) { /* If owner changed, trylock again. */ @@ -1421,11 +1425,27 @@ static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, * for CONFIG_PREEMPT_RCU=y) * - the VCPU on which owner runs is preempted */ - if (!owner_on_cpu(owner) || need_resched() || - !rt_mutex_waiter_is_top_waiter(lock, waiter)) { + if (!owner_on_cpu(owner) || need_resched()) { res = false; break; } + top_waiter = rt_mutex_top_waiter(lock); + if (top_waiter != waiter) { + if (top_waiter != last_waiter) { + raw_spin_lock_irq(&lock->wait_lock); + last_waiter = rt_mutex_top_waiter(lock); + top_task = last_waiter->task; + raw_spin_unlock_irq(&lock->wait_lock); + } + trace_printk("spin on owner! %s:%d\n", + top_task->comm, + top_task->pid); + + if (!owner_on_cpu(top_task)) { + res = false; + break; + } + } cpu_relax(); } rcu_read_unlock();
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