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![Steven Rostedt](/assets/img/avatar_default.png)
The smp_call_function can be passed a wait parameter telling it to wait for all the functions running on other CPUs to complete before returning, or to return without waiting. Unfortunately, this is currently just a suggestion and not manditory. That is, the smp_call_function can decide not to return and wait instead. The reason for this is because it uses kmalloc to allocate storage to send to the called CPU and that CPU will free it when it is done. But if we fail to allocate the storage, the stack is used instead. This means we must wait for the called CPU to finish before continuing. Unfortunatly, some callers do no abide by this hint and act as if the non-wait option is mandatory. The MTRR code for instance will deadlock if the smp_call_function is set to wait. This is because the smp_call_function will wait for the other CPUs to finish their called functions, but those functions are waiting on the caller to continue. This patch changes the generic smp_call_function code to use per cpu variables if the allocation of the data fails for a single CPU call. The smp_call_function_many will fall back to the smp_call_function_single if it fails its alloc. The smp_call_function_single is modified to not force the wait state. Since we now are using a single data per cpu we must synchronize the callers to prevent a second caller modifying the data before the first called IPI functions complete. To do so, I added a flag to the call_single_data called CSD_FLAG_LOCK. When the single CPU is called (which can be called when a many call fails an alloc), we set the LOCK bit on this per cpu data. When the caller finishes it clears the LOCK bit. The caller must wait till the LOCK bit is cleared before setting it. When it is cleared, there is no IPI function using it. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Jens Axboe <jens.axboe@oracle.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
432 lines
11 KiB
C
432 lines
11 KiB
C
/*
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* Generic helpers for smp ipi calls
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*
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* (C) Jens Axboe <jens.axboe@oracle.com> 2008
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*
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*/
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/percpu.h>
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#include <linux/rcupdate.h>
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#include <linux/rculist.h>
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#include <linux/smp.h>
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static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
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static LIST_HEAD(call_function_queue);
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__cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock);
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enum {
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CSD_FLAG_WAIT = 0x01,
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CSD_FLAG_ALLOC = 0x02,
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CSD_FLAG_LOCK = 0x04,
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};
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struct call_function_data {
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struct call_single_data csd;
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spinlock_t lock;
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unsigned int refs;
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struct rcu_head rcu_head;
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unsigned long cpumask_bits[];
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};
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struct call_single_queue {
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struct list_head list;
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spinlock_t lock;
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};
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static int __cpuinit init_call_single_data(void)
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{
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int i;
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for_each_possible_cpu(i) {
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struct call_single_queue *q = &per_cpu(call_single_queue, i);
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spin_lock_init(&q->lock);
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INIT_LIST_HEAD(&q->list);
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}
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return 0;
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}
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early_initcall(init_call_single_data);
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static void csd_flag_wait(struct call_single_data *data)
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{
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/* Wait for response */
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do {
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if (!(data->flags & CSD_FLAG_WAIT))
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break;
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cpu_relax();
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} while (1);
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}
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/*
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* Insert a previously allocated call_single_data element for execution
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* on the given CPU. data must already have ->func, ->info, and ->flags set.
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*/
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static void generic_exec_single(int cpu, struct call_single_data *data)
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{
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struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
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int wait = data->flags & CSD_FLAG_WAIT, ipi;
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unsigned long flags;
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spin_lock_irqsave(&dst->lock, flags);
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ipi = list_empty(&dst->list);
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list_add_tail(&data->list, &dst->list);
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spin_unlock_irqrestore(&dst->lock, flags);
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/*
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* Make the list addition visible before sending the ipi.
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*/
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smp_mb();
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if (ipi)
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arch_send_call_function_single_ipi(cpu);
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if (wait)
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csd_flag_wait(data);
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}
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static void rcu_free_call_data(struct rcu_head *head)
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{
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struct call_function_data *data;
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data = container_of(head, struct call_function_data, rcu_head);
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kfree(data);
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}
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/*
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* Invoked by arch to handle an IPI for call function. Must be called with
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* interrupts disabled.
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*/
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void generic_smp_call_function_interrupt(void)
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{
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struct call_function_data *data;
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int cpu = get_cpu();
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/*
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* It's ok to use list_for_each_rcu() here even though we may delete
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* 'pos', since list_del_rcu() doesn't clear ->next
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*/
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rcu_read_lock();
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list_for_each_entry_rcu(data, &call_function_queue, csd.list) {
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int refs;
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if (!cpumask_test_cpu(cpu, to_cpumask(data->cpumask_bits)))
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continue;
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data->csd.func(data->csd.info);
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spin_lock(&data->lock);
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cpumask_clear_cpu(cpu, to_cpumask(data->cpumask_bits));
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WARN_ON(data->refs == 0);
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data->refs--;
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refs = data->refs;
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spin_unlock(&data->lock);
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if (refs)
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continue;
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spin_lock(&call_function_lock);
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list_del_rcu(&data->csd.list);
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spin_unlock(&call_function_lock);
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if (data->csd.flags & CSD_FLAG_WAIT) {
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/*
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* serialize stores to data with the flag clear
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* and wakeup
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*/
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smp_wmb();
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data->csd.flags &= ~CSD_FLAG_WAIT;
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}
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if (data->csd.flags & CSD_FLAG_ALLOC)
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call_rcu(&data->rcu_head, rcu_free_call_data);
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}
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rcu_read_unlock();
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put_cpu();
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}
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/*
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* Invoked by arch to handle an IPI for call function single. Must be called
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* from the arch with interrupts disabled.
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*/
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void generic_smp_call_function_single_interrupt(void)
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{
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struct call_single_queue *q = &__get_cpu_var(call_single_queue);
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LIST_HEAD(list);
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/*
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* Need to see other stores to list head for checking whether
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* list is empty without holding q->lock
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*/
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smp_read_barrier_depends();
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while (!list_empty(&q->list)) {
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unsigned int data_flags;
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spin_lock(&q->lock);
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list_replace_init(&q->list, &list);
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spin_unlock(&q->lock);
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while (!list_empty(&list)) {
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struct call_single_data *data;
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data = list_entry(list.next, struct call_single_data,
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list);
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list_del(&data->list);
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/*
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* 'data' can be invalid after this call if
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* flags == 0 (when called through
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* generic_exec_single(), so save them away before
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* making the call.
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*/
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data_flags = data->flags;
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data->func(data->info);
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if (data_flags & CSD_FLAG_WAIT) {
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smp_wmb();
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data->flags &= ~CSD_FLAG_WAIT;
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} else if (data_flags & CSD_FLAG_LOCK) {
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smp_wmb();
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data->flags &= ~CSD_FLAG_LOCK;
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} else if (data_flags & CSD_FLAG_ALLOC)
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kfree(data);
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}
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/*
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* See comment on outer loop
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*/
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smp_read_barrier_depends();
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}
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}
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static DEFINE_PER_CPU(struct call_single_data, csd_data);
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/*
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* smp_call_function_single - Run a function on a specific CPU
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* @func: The function to run. This must be fast and non-blocking.
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* @info: An arbitrary pointer to pass to the function.
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* @wait: If true, wait until function has completed on other CPUs.
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*
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* Returns 0 on success, else a negative status code. Note that @wait
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* will be implicitly turned on in case of allocation failures, since
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* we fall back to on-stack allocation.
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*/
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int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
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int wait)
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{
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struct call_single_data d;
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unsigned long flags;
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/* prevent preemption and reschedule on another processor,
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as well as CPU removal */
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int me = get_cpu();
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int err = 0;
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/* Can deadlock when called with interrupts disabled */
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WARN_ON(irqs_disabled());
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if (cpu == me) {
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local_irq_save(flags);
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func(info);
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local_irq_restore(flags);
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} else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
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struct call_single_data *data;
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if (!wait) {
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/*
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* We are calling a function on a single CPU
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* and we are not going to wait for it to finish.
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* We first try to allocate the data, but if we
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* fail, we fall back to use a per cpu data to pass
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* the information to that CPU. Since all callers
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* of this code will use the same data, we must
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* synchronize the callers to prevent a new caller
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* from corrupting the data before the callee
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* can access it.
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*
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* The CSD_FLAG_LOCK is used to let us know when
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* the IPI handler is done with the data.
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* The first caller will set it, and the callee
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* will clear it. The next caller must wait for
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* it to clear before we set it again. This
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* will make sure the callee is done with the
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* data before a new caller will use it.
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*/
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data = kmalloc(sizeof(*data), GFP_ATOMIC);
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if (data)
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data->flags = CSD_FLAG_ALLOC;
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else {
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data = &per_cpu(csd_data, me);
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while (data->flags & CSD_FLAG_LOCK)
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cpu_relax();
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data->flags = CSD_FLAG_LOCK;
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}
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} else {
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data = &d;
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data->flags = CSD_FLAG_WAIT;
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}
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data->func = func;
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data->info = info;
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generic_exec_single(cpu, data);
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} else {
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err = -ENXIO; /* CPU not online */
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}
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put_cpu();
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return err;
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}
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EXPORT_SYMBOL(smp_call_function_single);
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/**
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* __smp_call_function_single(): Run a function on another CPU
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* @cpu: The CPU to run on.
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* @data: Pre-allocated and setup data structure
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*
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* Like smp_call_function_single(), but allow caller to pass in a pre-allocated
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* data structure. Useful for embedding @data inside other structures, for
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* instance.
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*
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*/
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void __smp_call_function_single(int cpu, struct call_single_data *data)
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{
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/* Can deadlock when called with interrupts disabled */
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WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());
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generic_exec_single(cpu, data);
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}
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/* FIXME: Shim for archs using old arch_send_call_function_ipi API. */
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#ifndef arch_send_call_function_ipi_mask
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#define arch_send_call_function_ipi_mask(maskp) \
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arch_send_call_function_ipi(*(maskp))
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#endif
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/**
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* smp_call_function_many(): Run a function on a set of other CPUs.
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* @mask: The set of cpus to run on (only runs on online subset).
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* @func: The function to run. This must be fast and non-blocking.
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* @info: An arbitrary pointer to pass to the function.
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* @wait: If true, wait (atomically) until function has completed on other CPUs.
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*
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* If @wait is true, then returns once @func has returned. Note that @wait
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* will be implicitly turned on in case of allocation failures, since
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* we fall back to on-stack allocation.
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*
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* You must not call this function with disabled interrupts or from a
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* hardware interrupt handler or from a bottom half handler. Preemption
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* must be disabled when calling this function.
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*/
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void smp_call_function_many(const struct cpumask *mask,
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void (*func)(void *), void *info,
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bool wait)
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{
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struct call_function_data *data;
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unsigned long flags;
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int cpu, next_cpu;
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/* Can deadlock when called with interrupts disabled */
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WARN_ON(irqs_disabled());
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/* So, what's a CPU they want? Ignoring this one. */
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cpu = cpumask_first_and(mask, cpu_online_mask);
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if (cpu == smp_processor_id())
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cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
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/* No online cpus? We're done. */
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if (cpu >= nr_cpu_ids)
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return;
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/* Do we have another CPU which isn't us? */
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next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
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if (next_cpu == smp_processor_id())
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next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
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/* Fastpath: do that cpu by itself. */
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if (next_cpu >= nr_cpu_ids) {
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smp_call_function_single(cpu, func, info, wait);
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return;
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}
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data = kmalloc(sizeof(*data) + cpumask_size(), GFP_ATOMIC);
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if (unlikely(!data)) {
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/* Slow path. */
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for_each_online_cpu(cpu) {
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if (cpu == smp_processor_id())
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continue;
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if (cpumask_test_cpu(cpu, mask))
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smp_call_function_single(cpu, func, info, wait);
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}
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return;
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}
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spin_lock_init(&data->lock);
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data->csd.flags = CSD_FLAG_ALLOC;
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if (wait)
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data->csd.flags |= CSD_FLAG_WAIT;
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data->csd.func = func;
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data->csd.info = info;
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cpumask_and(to_cpumask(data->cpumask_bits), mask, cpu_online_mask);
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cpumask_clear_cpu(smp_processor_id(), to_cpumask(data->cpumask_bits));
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data->refs = cpumask_weight(to_cpumask(data->cpumask_bits));
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spin_lock_irqsave(&call_function_lock, flags);
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list_add_tail_rcu(&data->csd.list, &call_function_queue);
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spin_unlock_irqrestore(&call_function_lock, flags);
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/*
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* Make the list addition visible before sending the ipi.
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*/
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smp_mb();
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/* Send a message to all CPUs in the map */
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arch_send_call_function_ipi_mask(to_cpumask(data->cpumask_bits));
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/* optionally wait for the CPUs to complete */
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if (wait)
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csd_flag_wait(&data->csd);
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}
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EXPORT_SYMBOL(smp_call_function_many);
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/**
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* smp_call_function(): Run a function on all other CPUs.
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* @func: The function to run. This must be fast and non-blocking.
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* @info: An arbitrary pointer to pass to the function.
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* @wait: If true, wait (atomically) until function has completed on other CPUs.
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*
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* Returns 0.
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*
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* If @wait is true, then returns once @func has returned; otherwise
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* it returns just before the target cpu calls @func. In case of allocation
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* failure, @wait will be implicitly turned on.
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*
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* You must not call this function with disabled interrupts or from a
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* hardware interrupt handler or from a bottom half handler.
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*/
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int smp_call_function(void (*func)(void *), void *info, int wait)
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{
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preempt_disable();
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smp_call_function_many(cpu_online_mask, func, info, wait);
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preempt_enable();
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return 0;
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}
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EXPORT_SYMBOL(smp_call_function);
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void ipi_call_lock(void)
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{
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spin_lock(&call_function_lock);
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}
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void ipi_call_unlock(void)
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{
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spin_unlock(&call_function_lock);
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}
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void ipi_call_lock_irq(void)
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{
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spin_lock_irq(&call_function_lock);
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}
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void ipi_call_unlock_irq(void)
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{
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spin_unlock_irq(&call_function_lock);
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}
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