mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-05 17:56:39 +07:00
ec6c676a08
(Trivial patch.) If the code is looking at the RCU-protected pointer itself, but not dereferencing it, the rcu_dereference() functions can be downgraded to rcu_access_pointer(). This commit makes this downgrade in blkg_destroy() and ioc_destroy_icq(), both of which simply compare the RCU-protected pointer against another pointer with no dereferencing. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Jens Axboe <axboe@fb.com>
408 lines
10 KiB
C
408 lines
10 KiB
C
/*
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* Functions related to io context handling
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/bio.h>
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#include <linux/blkdev.h>
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#include <linux/slab.h>
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#include "blk.h"
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/*
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* For io context allocations
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*/
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static struct kmem_cache *iocontext_cachep;
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/**
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* get_io_context - increment reference count to io_context
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* @ioc: io_context to get
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*
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* Increment reference count to @ioc.
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*/
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void get_io_context(struct io_context *ioc)
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{
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BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
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atomic_long_inc(&ioc->refcount);
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}
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EXPORT_SYMBOL(get_io_context);
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static void icq_free_icq_rcu(struct rcu_head *head)
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{
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struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
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kmem_cache_free(icq->__rcu_icq_cache, icq);
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}
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/* Exit an icq. Called with both ioc and q locked. */
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static void ioc_exit_icq(struct io_cq *icq)
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{
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struct elevator_type *et = icq->q->elevator->type;
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if (icq->flags & ICQ_EXITED)
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return;
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if (et->ops.elevator_exit_icq_fn)
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et->ops.elevator_exit_icq_fn(icq);
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icq->flags |= ICQ_EXITED;
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}
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/* Release an icq. Called with both ioc and q locked. */
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static void ioc_destroy_icq(struct io_cq *icq)
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{
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struct io_context *ioc = icq->ioc;
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struct request_queue *q = icq->q;
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struct elevator_type *et = q->elevator->type;
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lockdep_assert_held(&ioc->lock);
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lockdep_assert_held(q->queue_lock);
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radix_tree_delete(&ioc->icq_tree, icq->q->id);
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hlist_del_init(&icq->ioc_node);
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list_del_init(&icq->q_node);
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/*
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* Both setting lookup hint to and clearing it from @icq are done
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* under queue_lock. If it's not pointing to @icq now, it never
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* will. Hint assignment itself can race safely.
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*/
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if (rcu_access_pointer(ioc->icq_hint) == icq)
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rcu_assign_pointer(ioc->icq_hint, NULL);
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ioc_exit_icq(icq);
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/*
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* @icq->q might have gone away by the time RCU callback runs
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* making it impossible to determine icq_cache. Record it in @icq.
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*/
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icq->__rcu_icq_cache = et->icq_cache;
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call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
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}
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/*
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* Slow path for ioc release in put_io_context(). Performs double-lock
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* dancing to unlink all icq's and then frees ioc.
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*/
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static void ioc_release_fn(struct work_struct *work)
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{
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struct io_context *ioc = container_of(work, struct io_context,
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release_work);
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unsigned long flags;
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/*
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* Exiting icq may call into put_io_context() through elevator
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* which will trigger lockdep warning. The ioc's are guaranteed to
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* be different, use a different locking subclass here. Use
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* irqsave variant as there's no spin_lock_irq_nested().
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*/
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spin_lock_irqsave_nested(&ioc->lock, flags, 1);
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while (!hlist_empty(&ioc->icq_list)) {
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struct io_cq *icq = hlist_entry(ioc->icq_list.first,
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struct io_cq, ioc_node);
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struct request_queue *q = icq->q;
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if (spin_trylock(q->queue_lock)) {
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ioc_destroy_icq(icq);
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spin_unlock(q->queue_lock);
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} else {
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spin_unlock_irqrestore(&ioc->lock, flags);
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cpu_relax();
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spin_lock_irqsave_nested(&ioc->lock, flags, 1);
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}
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}
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spin_unlock_irqrestore(&ioc->lock, flags);
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kmem_cache_free(iocontext_cachep, ioc);
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}
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/**
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* put_io_context - put a reference of io_context
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* @ioc: io_context to put
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*
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* Decrement reference count of @ioc and release it if the count reaches
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* zero.
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*/
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void put_io_context(struct io_context *ioc)
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{
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unsigned long flags;
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bool free_ioc = false;
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if (ioc == NULL)
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return;
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BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
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/*
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* Releasing ioc requires reverse order double locking and we may
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* already be holding a queue_lock. Do it asynchronously from wq.
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*/
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if (atomic_long_dec_and_test(&ioc->refcount)) {
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spin_lock_irqsave(&ioc->lock, flags);
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if (!hlist_empty(&ioc->icq_list))
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queue_work(system_power_efficient_wq,
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&ioc->release_work);
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else
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free_ioc = true;
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spin_unlock_irqrestore(&ioc->lock, flags);
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}
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if (free_ioc)
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kmem_cache_free(iocontext_cachep, ioc);
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}
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EXPORT_SYMBOL(put_io_context);
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/**
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* put_io_context_active - put active reference on ioc
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* @ioc: ioc of interest
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*
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* Undo get_io_context_active(). If active reference reaches zero after
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* put, @ioc can never issue further IOs and ioscheds are notified.
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*/
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void put_io_context_active(struct io_context *ioc)
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{
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unsigned long flags;
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struct io_cq *icq;
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if (!atomic_dec_and_test(&ioc->active_ref)) {
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put_io_context(ioc);
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return;
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}
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/*
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* Need ioc lock to walk icq_list and q lock to exit icq. Perform
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* reverse double locking. Read comment in ioc_release_fn() for
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* explanation on the nested locking annotation.
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*/
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retry:
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spin_lock_irqsave_nested(&ioc->lock, flags, 1);
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hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
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if (icq->flags & ICQ_EXITED)
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continue;
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if (spin_trylock(icq->q->queue_lock)) {
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ioc_exit_icq(icq);
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spin_unlock(icq->q->queue_lock);
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} else {
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spin_unlock_irqrestore(&ioc->lock, flags);
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cpu_relax();
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goto retry;
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}
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}
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spin_unlock_irqrestore(&ioc->lock, flags);
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put_io_context(ioc);
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}
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/* Called by the exiting task */
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void exit_io_context(struct task_struct *task)
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{
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struct io_context *ioc;
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task_lock(task);
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ioc = task->io_context;
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task->io_context = NULL;
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task_unlock(task);
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atomic_dec(&ioc->nr_tasks);
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put_io_context_active(ioc);
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}
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/**
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* ioc_clear_queue - break any ioc association with the specified queue
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* @q: request_queue being cleared
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*
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* Walk @q->icq_list and exit all io_cq's. Must be called with @q locked.
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*/
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void ioc_clear_queue(struct request_queue *q)
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{
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lockdep_assert_held(q->queue_lock);
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while (!list_empty(&q->icq_list)) {
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struct io_cq *icq = list_entry(q->icq_list.next,
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struct io_cq, q_node);
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struct io_context *ioc = icq->ioc;
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spin_lock(&ioc->lock);
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ioc_destroy_icq(icq);
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spin_unlock(&ioc->lock);
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}
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}
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int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
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{
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struct io_context *ioc;
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int ret;
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ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
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node);
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if (unlikely(!ioc))
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return -ENOMEM;
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/* initialize */
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atomic_long_set(&ioc->refcount, 1);
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atomic_set(&ioc->nr_tasks, 1);
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atomic_set(&ioc->active_ref, 1);
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spin_lock_init(&ioc->lock);
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INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
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INIT_HLIST_HEAD(&ioc->icq_list);
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INIT_WORK(&ioc->release_work, ioc_release_fn);
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/*
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* Try to install. ioc shouldn't be installed if someone else
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* already did or @task, which isn't %current, is exiting. Note
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* that we need to allow ioc creation on exiting %current as exit
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* path may issue IOs from e.g. exit_files(). The exit path is
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* responsible for not issuing IO after exit_io_context().
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*/
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task_lock(task);
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if (!task->io_context &&
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(task == current || !(task->flags & PF_EXITING)))
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task->io_context = ioc;
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else
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kmem_cache_free(iocontext_cachep, ioc);
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ret = task->io_context ? 0 : -EBUSY;
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task_unlock(task);
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return ret;
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}
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/**
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* get_task_io_context - get io_context of a task
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* @task: task of interest
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* @gfp_flags: allocation flags, used if allocation is necessary
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* @node: allocation node, used if allocation is necessary
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*
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* Return io_context of @task. If it doesn't exist, it is created with
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* @gfp_flags and @node. The returned io_context has its reference count
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* incremented.
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*
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* This function always goes through task_lock() and it's better to use
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* %current->io_context + get_io_context() for %current.
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*/
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struct io_context *get_task_io_context(struct task_struct *task,
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gfp_t gfp_flags, int node)
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{
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struct io_context *ioc;
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might_sleep_if(gfp_flags & __GFP_WAIT);
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do {
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task_lock(task);
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ioc = task->io_context;
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if (likely(ioc)) {
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get_io_context(ioc);
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task_unlock(task);
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return ioc;
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}
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task_unlock(task);
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} while (!create_task_io_context(task, gfp_flags, node));
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return NULL;
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}
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EXPORT_SYMBOL(get_task_io_context);
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/**
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* ioc_lookup_icq - lookup io_cq from ioc
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* @ioc: the associated io_context
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* @q: the associated request_queue
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*
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* Look up io_cq associated with @ioc - @q pair from @ioc. Must be called
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* with @q->queue_lock held.
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*/
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struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
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{
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struct io_cq *icq;
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lockdep_assert_held(q->queue_lock);
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/*
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* icq's are indexed from @ioc using radix tree and hint pointer,
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* both of which are protected with RCU. All removals are done
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* holding both q and ioc locks, and we're holding q lock - if we
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* find a icq which points to us, it's guaranteed to be valid.
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*/
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rcu_read_lock();
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icq = rcu_dereference(ioc->icq_hint);
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if (icq && icq->q == q)
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goto out;
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icq = radix_tree_lookup(&ioc->icq_tree, q->id);
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if (icq && icq->q == q)
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rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
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else
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icq = NULL;
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out:
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rcu_read_unlock();
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return icq;
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}
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EXPORT_SYMBOL(ioc_lookup_icq);
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/**
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* ioc_create_icq - create and link io_cq
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* @ioc: io_context of interest
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* @q: request_queue of interest
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* @gfp_mask: allocation mask
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*
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* Make sure io_cq linking @ioc and @q exists. If icq doesn't exist, they
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* will be created using @gfp_mask.
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*
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* The caller is responsible for ensuring @ioc won't go away and @q is
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* alive and will stay alive until this function returns.
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*/
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struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
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gfp_t gfp_mask)
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{
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struct elevator_type *et = q->elevator->type;
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struct io_cq *icq;
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/* allocate stuff */
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icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
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q->node);
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if (!icq)
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return NULL;
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if (radix_tree_maybe_preload(gfp_mask) < 0) {
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kmem_cache_free(et->icq_cache, icq);
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return NULL;
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}
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icq->ioc = ioc;
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icq->q = q;
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INIT_LIST_HEAD(&icq->q_node);
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INIT_HLIST_NODE(&icq->ioc_node);
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/* lock both q and ioc and try to link @icq */
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spin_lock_irq(q->queue_lock);
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spin_lock(&ioc->lock);
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if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
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hlist_add_head(&icq->ioc_node, &ioc->icq_list);
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list_add(&icq->q_node, &q->icq_list);
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if (et->ops.elevator_init_icq_fn)
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et->ops.elevator_init_icq_fn(icq);
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} else {
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kmem_cache_free(et->icq_cache, icq);
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icq = ioc_lookup_icq(ioc, q);
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if (!icq)
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printk(KERN_ERR "cfq: icq link failed!\n");
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}
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spin_unlock(&ioc->lock);
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spin_unlock_irq(q->queue_lock);
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radix_tree_preload_end();
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return icq;
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}
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static int __init blk_ioc_init(void)
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{
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iocontext_cachep = kmem_cache_create("blkdev_ioc",
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sizeof(struct io_context), 0, SLAB_PANIC, NULL);
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return 0;
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}
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subsys_initcall(blk_ioc_init);
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