/*
* Functions related to io context handling
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/bootmem.h> /* for max_pfn/max_low_pfn */
#include <linux/slab.h>
#include "blk.h"
/*
* For io context allocations
*/
static struct kmem_cache *iocontext_cachep;
/**
* get_io_context - increment reference count to io_context
* @ioc: io_context to get
*
* Increment reference count to @ioc.
*/
void get_io_context(struct io_context *ioc)
{
BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
atomic_long_inc(&ioc->refcount);
}
EXPORT_SYMBOL(get_io_context);
/*
* Releasing ioc may nest into another put_io_context() leading to nested
* fast path release. As the ioc's can't be the same, this is okay but
* makes lockdep whine. Keep track of nesting and use it as subclass.
*/
#ifdef CONFIG_LOCKDEP
#define ioc_release_depth(q) ((q) ? (q)->ioc_release_depth : 0)
#define ioc_release_depth_inc(q) (q)->ioc_release_depth++
#define ioc_release_depth_dec(q) (q)->ioc_release_depth--
#else
#define ioc_release_depth(q) 0
#define ioc_release_depth_inc(q) do { } while (0)
#define ioc_release_depth_dec(q) do { } while (0)
#endif
/*
* Slow path for ioc release in put_io_context(). Performs double-lock
* dancing to unlink all cic's and then frees ioc.
*/
static void ioc_release_fn(struct work_struct *work)
{
struct io_context *ioc = container_of(work, struct io_context,
release_work);
struct request_queue *last_q = NULL;
spin_lock_irq(&ioc->lock);
while (!hlist_empty(&ioc->cic_list)) {
struct cfq_io_context *cic = hlist_entry(ioc->cic_list.first,
struct cfq_io_context,
cic_list);
struct request_queue *this_q = cic->q;
if (this_q != last_q) {
/*
* Need to switch to @this_q. Once we release
* @ioc->lock, it can go away along with @cic.
* Hold on to it.
*/
__blk_get_queue(this_q);
/*
* blk_put_queue() might sleep thanks to kobject
* idiocy. Always release both locks, put and
* restart.
*/
if (last_q) {
spin_unlock(last_q->queue_lock);
spin_unlock_irq(&ioc->lock);
blk_put_queue(last_q);
} else {
spin_unlock_irq(&ioc->lock);
}
last_q = this_q;
spin_lock_irq(this_q->queue_lock);
spin_lock(&ioc->lock);
continue;
}
ioc_release_depth_inc(this_q);
cic->exit(cic);
cic->release(cic);
ioc_release_depth_dec(this_q);
}
if (last_q) {
spin_unlock(last_q->queue_lock);
spin_unlock_irq(&ioc->lock);
blk_put_queue(last_q);
} else {
spin_unlock_irq(&ioc->lock);
}
kmem_cache_free(iocontext_cachep, ioc);
}
/**
* put_io_context - put a reference of io_context
* @ioc: io_context to put
* @locked_q: request_queue the caller is holding queue_lock of (hint)
*
* Decrement reference count of @ioc and release it if the count reaches
* zero. If the caller is holding queue_lock of a queue, it can indicate
* that with @locked_q. This is an optimization hint and the caller is
* allowed to pass in %NULL even when it's holding a queue_lock.
*/
void put_io_context(struct io_context *ioc, struct request_queue *locked_q)
{
struct request_queue *last_q = locked_q;
unsigned long flags;
if (ioc == NULL)
return;
BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
if (locked_q)
lockdep_assert_held(locked_q->queue_lock);
if (!atomic_long_dec_and_test(&ioc->refcount))
return;
/*
* Destroy @ioc. This is a bit messy because cic's are chained
* from both ioc and queue, and ioc->lock nests inside queue_lock.
* The inner ioc->lock should be held to walk our cic_list and then
* for each cic the outer matching queue_lock should be grabbed.
* ie. We need to do reverse-order double lock dancing.
*
* Another twist is that we are often called with one of the
* matching queue_locks held as indicated by @locked_q, which
* prevents performing double-lock dance for other queues.
*
* So, we do it in two stages. The fast path uses the queue_lock
* the caller is holding and, if other queues need to be accessed,
* uses trylock to avoid introducing locking dependency. This can
* handle most cases, especially if @ioc was performing IO on only
* single device.
*
* If trylock doesn't cut it, we defer to @ioc->release_work which
* can do all the double-locking dancing.
*/
spin_lock_irqsave_nested(&ioc->lock, flags,
ioc_release_depth(locked_q));
while (!hlist_empty(&ioc->cic_list)) {
struct cfq_io_context *cic = hlist_entry(ioc->cic_list.first,
struct cfq_io_context,
cic_list);
struct request_queue *this_q = cic->q;
if (this_q != last_q) {
if (last_q && last_q != locked_q)
spin_unlock(last_q->queue_lock);
last_q = NULL;
if (!spin_trylock(this_q->queue_lock))
break;
last_q = this_q;
continue;
}
ioc_release_depth_inc(this_q);
cic->exit(cic);
cic->release(cic);
ioc_release_depth_dec(this_q);
}
if (last_q && last_q != locked_q)
spin_unlock(last_q->queue_lock);
spin_unlock_irqrestore(&ioc->lock, flags);
/* if no cic's left, we're done; otherwise, kick release_work */
if (hlist_empty(&ioc->cic_list))
kmem_cache_free(iocontext_cachep, ioc);
else
schedule_work(&ioc->release_work);
}
EXPORT_SYMBOL(put_io_context);
/* Called by the exiting task */
void exit_io_context(struct task_struct *task)
{
struct io_context *ioc;
/* PF_EXITING prevents new io_context from being attached to @task */
WARN_ON_ONCE(!(current->flags & PF_EXITING));
task_lock(task);
ioc = task->io_context;
task->io_context = NULL;
task_unlock(task);
atomic_dec(&ioc->nr_tasks);
put_io_context(ioc, NULL);
}
static struct io_context *create_task_io_context(struct task_struct *task,
gfp_t gfp_flags, int node,
bool take_ref)
{
struct io_context *ioc;
ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
node);
if (unlikely(!ioc))
return NULL;
/* initialize */
atomic_long_set(&ioc->refcount, 1);
atomic_set(&ioc->nr_tasks, 1);
spin_lock_init(&ioc->lock);
INIT_RADIX_TREE(&ioc->radix_root, GFP_ATOMIC | __GFP_HIGH);
INIT_HLIST_HEAD(&ioc->cic_list);
INIT_WORK(&ioc->release_work, ioc_release_fn);
/* try to install, somebody might already have beaten us to it */
task_lock(task);
if (!task->io_context && !(task->flags & PF_EXITING)) {
task->io_context = ioc;
} else {
kmem_cache_free(iocontext_cachep, ioc);
ioc = task->io_context;
}
if (ioc && take_ref)
get_io_context(ioc);
task_unlock(task);
return ioc;
}
/**
* current_io_context - get io_context of %current
* @gfp_flags: allocation flags, used if allocation is necessary
* @node: allocation node, used if allocation is necessary
*
* Return io_context of %current. If it doesn't exist, it is created with
* @gfp_flags and @node. The returned io_context does NOT have its
* reference count incremented. Because io_context is exited only on task
* exit, %current can be sure that the returned io_context is valid and
* alive as long as it is executing.
*/
struct io_context *current_io_context(gfp_t gfp_flags, int node)
{
might_sleep_if(gfp_flags & __GFP_WAIT);
if (current->io_context)
return current->io_context;
return create_task_io_context(current, gfp_flags, node, false);
}
EXPORT_SYMBOL(current_io_context);
/**
* get_task_io_context - get io_context of a task
* @task: task of interest
* @gfp_flags: allocation flags, used if allocation is necessary
* @node: allocation node, used if allocation is necessary
*
* Return io_context of @task. If it doesn't exist, it is created with
* @gfp_flags and @node. The returned io_context has its reference count
* incremented.
*
* This function always goes through task_lock() and it's better to use
* current_io_context() + get_io_context() for %current.
*/
struct io_context *get_task_io_context(struct task_struct *task,
gfp_t gfp_flags, int node)
{
struct io_context *ioc;
might_sleep_if(gfp_flags & __GFP_WAIT);
task_lock(task);
ioc = task->io_context;
if (likely(ioc)) {
get_io_context(ioc);
task_unlock(task);
return ioc;
}
task_unlock(task);
return create_task_io_context(task, gfp_flags, node, true);
}
EXPORT_SYMBOL(get_task_io_context);
void ioc_set_changed(struct io_context *ioc, int which)
{
struct cfq_io_context *cic;
struct hlist_node *n;
hlist_for_each_entry(cic, n, &ioc->cic_list, cic_list)
set_bit(which, &cic->changed);
}
/**
* ioc_ioprio_changed - notify ioprio change
* @ioc: io_context of interest
* @ioprio: new ioprio
*
* @ioc's ioprio has changed to @ioprio. Set %CIC_IOPRIO_CHANGED for all
* cic's. iosched is responsible for checking the bit and applying it on
* request issue path.
*/
void ioc_ioprio_changed(struct io_context *ioc, int ioprio)
{
unsigned long flags;
spin_lock_irqsave(&ioc->lock, flags);
ioc->ioprio = ioprio;
ioc_set_changed(ioc, CIC_IOPRIO_CHANGED);
spin_unlock_irqrestore(&ioc->lock, flags);
}
/**
* ioc_cgroup_changed - notify cgroup change
* @ioc: io_context of interest
*
* @ioc's cgroup has changed. Set %CIC_CGROUP_CHANGED for all cic's.
* iosched is responsible for checking the bit and applying it on request
* issue path.
*/
void ioc_cgroup_changed(struct io_context *ioc)
{
unsigned long flags;
spin_lock_irqsave(&ioc->lock, flags);
ioc_set_changed(ioc, CIC_CGROUP_CHANGED);
spin_unlock_irqrestore(&ioc->lock, flags);
}
static int __init blk_ioc_init(void)
{
iocontext_cachep = kmem_cache_create("blkdev_ioc",
sizeof(struct io_context), 0, SLAB_PANIC, NULL);
return 0;
}
subsys_initcall(blk_ioc_init);
