The following commit has been merged into the core/rcu branch of tip: Commit-ID: 8ac88f7177c75bf9b7b8c29a8054115e1c712baf Gitweb: https://git.kernel.org/tip/8ac88f7177c75bf9b7b8c29a8054115e1c712baf Author: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> AuthorDate: Mon, 25 May 2020 23:47:45 +02:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Mon, 29 Jun 2020 11:59:25 -07:00 rcu/tree: Keep kfree_rcu() awake during lock contention On PREEMPT_RT kernels, the krcp spinlock gets converted to an rt-mutex and causes kfree_rcu() callers to sleep. This makes it unusable for callers in purely atomic sections such as non-threaded IRQ handlers and raw spinlock sections. Fix it by converting the spinlock to a raw spinlock. Vetting all code paths, there is no reason to believe that the raw spinlock will hurt RT latencies as it is not held for a long time. Cc: bigeasy@xxxxxxxxxxxxx Cc: Uladzislau Rezki <urezki@xxxxxxxxx> Reviewed-by: Uladzislau Rezki <urezki@xxxxxxxxx> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- kernel/rcu/tree.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index ba4c477..c5de5ad 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3016,7 +3016,7 @@ struct kfree_rcu_cpu { struct kfree_rcu_bulk_data *bhead; struct kfree_rcu_bulk_data *bcached; struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES]; - spinlock_t lock; + raw_spinlock_t lock; struct delayed_work monitor_work; bool monitor_todo; bool initialized; @@ -3049,12 +3049,12 @@ static void kfree_rcu_work(struct work_struct *work) krwp = container_of(to_rcu_work(work), struct kfree_rcu_cpu_work, rcu_work); krcp = krwp->krcp; - spin_lock_irqsave(&krcp->lock, flags); + raw_spin_lock_irqsave(&krcp->lock, flags); head = krwp->head_free; krwp->head_free = NULL; bhead = krwp->bhead_free; krwp->bhead_free = NULL; - spin_unlock_irqrestore(&krcp->lock, flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); /* "bhead" is now private, so traverse locklessly. */ for (; bhead; bhead = bnext) { @@ -3157,14 +3157,14 @@ static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp, krcp->monitor_todo = false; if (queue_kfree_rcu_work(krcp)) { // Success! Our job is done here. - spin_unlock_irqrestore(&krcp->lock, flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); return; } // Previous RCU batch still in progress, try again later. krcp->monitor_todo = true; schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES); - spin_unlock_irqrestore(&krcp->lock, flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); } /* @@ -3177,11 +3177,11 @@ static void kfree_rcu_monitor(struct work_struct *work) struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu, monitor_work.work); - spin_lock_irqsave(&krcp->lock, flags); + raw_spin_lock_irqsave(&krcp->lock, flags); if (krcp->monitor_todo) kfree_rcu_drain_unlock(krcp, flags); else - spin_unlock_irqrestore(&krcp->lock, flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); } static inline bool @@ -3252,7 +3252,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) local_irq_save(flags); // For safely calling this_cpu_ptr(). krcp = this_cpu_ptr(&krc); if (krcp->initialized) - spin_lock(&krcp->lock); + raw_spin_lock(&krcp->lock); // Queue the object but don't yet schedule the batch. if (debug_rcu_head_queue(head)) { @@ -3283,7 +3283,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) unlock_return: if (krcp->initialized) - spin_unlock(&krcp->lock); + raw_spin_unlock(&krcp->lock); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(kfree_call_rcu); @@ -3315,11 +3315,11 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); count = krcp->count; - spin_lock_irqsave(&krcp->lock, flags); + raw_spin_lock_irqsave(&krcp->lock, flags); if (krcp->monitor_todo) kfree_rcu_drain_unlock(krcp, flags); else - spin_unlock_irqrestore(&krcp->lock, flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); sc->nr_to_scan -= count; freed += count; @@ -3346,15 +3346,15 @@ void __init kfree_rcu_scheduler_running(void) for_each_online_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); - spin_lock_irqsave(&krcp->lock, flags); + raw_spin_lock_irqsave(&krcp->lock, flags); if (!krcp->head || krcp->monitor_todo) { - spin_unlock_irqrestore(&krcp->lock, flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); continue; } krcp->monitor_todo = true; schedule_delayed_work_on(cpu, &krcp->monitor_work, KFREE_DRAIN_JIFFIES); - spin_unlock_irqrestore(&krcp->lock, flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); } } @@ -4250,7 +4250,7 @@ static void __init kfree_rcu_batch_init(void) for_each_possible_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); - spin_lock_init(&krcp->lock); + raw_spin_lock_init(&krcp->lock); for (i = 0; i < KFREE_N_BATCHES; i++) { INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work); krcp->krw_arr[i].krcp = krcp;
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