blkcg: shoot down blkio_groups on elevator switch

Elevator switch may involve changes to blkcg policies.  Implement
shoot down of blkio_groups.

Combined with the previous bypass updates, the end goal is updating
blkcg core such that it can ensure that blkcg's being affected become
quiescent and don't have any per-blkg data hanging around before
commencing any policy updates.  Until queues are made aware of the
policies that applies to them, as an interim step, all per-policy blkg
data will be shot down.

* blk-throtl doesn't need this change as it can't be disabled for a
  live queue; however, update it anyway as the scheduled blkg
  unification requires this behavior change.  This means that
  blk-throtl configuration will be unnecessarily lost over elevator
  switch.  This oddity will be removed after blkcg learns to associate
  individual policies with request_queues.

* blk-throtl dosen't shoot down root_tg.  This is to ease transition.
  Unified blkg will always have persistent root group and not shooting
  down root_tg for now eases transition to that point by avoiding
  having to update td->root_tg and is safe as blk-throtl can never be
  disabled

-v2: Vivek pointed out that group list is not guaranteed to be empty
     on return from clear function if it raced cgroup removal and
     lost.  Fix it by waiting a bit and retrying.  This kludge will
     soon be removed once locking is updated such that blkg is never
     in limbo state between blkcg and request_queue locks.

     blk-throtl no longer shoots down root_tg to avoid breaking
     td->root_tg.

     Also, Nest queue_lock inside blkio_list_lock not the other way
     around to avoid introduce possible deadlock via blkcg lock.

-v3: blkcg_clear_queue() repositioned and renamed to
     blkg_destroy_all() to increase consistency with later changes.
     cfq_clear_queue() updated to check q->elevator before
     dereferencing it to avoid NULL dereference on not fully
     initialized queues (used by later change).

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo 2012-03-05 13:15:00 -08:00 committed by Jens Axboe
parent 6ecf23afab
commit 72e06c2551
5 changed files with 84 additions and 5 deletions

View File

@ -17,8 +17,9 @@
#include <linux/err.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include "blk-cgroup.h"
#include <linux/genhd.h>
#include <linux/delay.h>
#include "blk-cgroup.h"
#define MAX_KEY_LEN 100
@ -546,6 +547,37 @@ struct blkio_group *blkiocg_lookup_group(struct blkio_cgroup *blkcg, void *key)
}
EXPORT_SYMBOL_GPL(blkiocg_lookup_group);
void blkg_destroy_all(struct request_queue *q)
{
struct blkio_policy_type *pol;
while (true) {
bool done = true;
spin_lock(&blkio_list_lock);
spin_lock_irq(q->queue_lock);
/*
* clear_queue_fn() might return with non-empty group list
* if it raced cgroup removal and lost. cgroup removal is
* guaranteed to make forward progress and retrying after a
* while is enough. This ugliness is scheduled to be
* removed after locking update.
*/
list_for_each_entry(pol, &blkio_list, list)
if (!pol->ops.blkio_clear_queue_fn(q))
done = false;
spin_unlock_irq(q->queue_lock);
spin_unlock(&blkio_list_lock);
if (done)
break;
msleep(10); /* just some random duration I like */
}
}
static void blkio_reset_stats_cpu(struct blkio_group *blkg)
{
struct blkio_group_stats_cpu *stats_cpu;

View File

@ -203,7 +203,7 @@ extern unsigned int blkcg_get_write_iops(struct blkio_cgroup *blkcg,
dev_t dev);
typedef void (blkio_unlink_group_fn) (void *key, struct blkio_group *blkg);
typedef bool (blkio_clear_queue_fn)(struct request_queue *q);
typedef void (blkio_update_group_weight_fn) (void *key,
struct blkio_group *blkg, unsigned int weight);
typedef void (blkio_update_group_read_bps_fn) (void * key,
@ -217,6 +217,7 @@ typedef void (blkio_update_group_write_iops_fn) (void *key,
struct blkio_policy_ops {
blkio_unlink_group_fn *blkio_unlink_group_fn;
blkio_clear_queue_fn *blkio_clear_queue_fn;
blkio_update_group_weight_fn *blkio_update_group_weight_fn;
blkio_update_group_read_bps_fn *blkio_update_group_read_bps_fn;
blkio_update_group_write_bps_fn *blkio_update_group_write_bps_fn;
@ -233,6 +234,7 @@ struct blkio_policy_type {
/* Blkio controller policy registration */
extern void blkio_policy_register(struct blkio_policy_type *);
extern void blkio_policy_unregister(struct blkio_policy_type *);
extern void blkg_destroy_all(struct request_queue *q);
static inline char *blkg_path(struct blkio_group *blkg)
{
@ -249,6 +251,7 @@ struct blkio_policy_type {
static inline void blkio_policy_register(struct blkio_policy_type *blkiop) { }
static inline void blkio_policy_unregister(struct blkio_policy_type *blkiop) { }
static inline void blkg_destroy_all(struct request_queue *q) { }
static inline char *blkg_path(struct blkio_group *blkg) { return NULL; }

View File

@ -989,12 +989,17 @@ throtl_destroy_tg(struct throtl_data *td, struct throtl_grp *tg)
td->nr_undestroyed_grps--;
}
static void throtl_release_tgs(struct throtl_data *td)
static bool throtl_release_tgs(struct throtl_data *td, bool release_root)
{
struct hlist_node *pos, *n;
struct throtl_grp *tg;
bool empty = true;
hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
/* skip root? */
if (!release_root && tg == td->root_tg)
continue;
/*
* If cgroup removal path got to blk_group first and removed
* it from cgroup list, then it will take care of destroying
@ -1002,7 +1007,10 @@ static void throtl_release_tgs(struct throtl_data *td)
*/
if (!blkiocg_del_blkio_group(&tg->blkg))
throtl_destroy_tg(td, tg);
else
empty = false;
}
return empty;
}
/*
@ -1029,6 +1037,20 @@ void throtl_unlink_blkio_group(void *key, struct blkio_group *blkg)
spin_unlock_irqrestore(td->queue->queue_lock, flags);
}
static bool throtl_clear_queue(struct request_queue *q)
{
lockdep_assert_held(q->queue_lock);
/*
* Clear tgs but leave the root one alone. This is necessary
* because root_tg is expected to be persistent and safe because
* blk-throtl can never be disabled while @q is alive. This is a
* kludge to prepare for unified blkg. This whole function will be
* removed soon.
*/
return throtl_release_tgs(q->td, false);
}
static void throtl_update_blkio_group_common(struct throtl_data *td,
struct throtl_grp *tg)
{
@ -1097,6 +1119,7 @@ static void throtl_shutdown_wq(struct request_queue *q)
static struct blkio_policy_type blkio_policy_throtl = {
.ops = {
.blkio_unlink_group_fn = throtl_unlink_blkio_group,
.blkio_clear_queue_fn = throtl_clear_queue,
.blkio_update_group_read_bps_fn =
throtl_update_blkio_group_read_bps,
.blkio_update_group_write_bps_fn =
@ -1282,7 +1305,7 @@ void blk_throtl_exit(struct request_queue *q)
throtl_shutdown_wq(q);
spin_lock_irq(q->queue_lock);
throtl_release_tgs(td);
throtl_release_tgs(td, true);
/* If there are other groups */
if (td->nr_undestroyed_grps > 0)

View File

@ -1225,10 +1225,11 @@ static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg)
cfq_put_cfqg(cfqg);
}
static void cfq_release_cfq_groups(struct cfq_data *cfqd)
static bool cfq_release_cfq_groups(struct cfq_data *cfqd)
{
struct hlist_node *pos, *n;
struct cfq_group *cfqg;
bool empty = true;
hlist_for_each_entry_safe(cfqg, pos, n, &cfqd->cfqg_list, cfqd_node) {
/*
@ -1238,7 +1239,10 @@ static void cfq_release_cfq_groups(struct cfq_data *cfqd)
*/
if (!cfq_blkiocg_del_blkio_group(&cfqg->blkg))
cfq_destroy_cfqg(cfqd, cfqg);
else
empty = false;
}
return empty;
}
/*
@ -1265,6 +1269,19 @@ static void cfq_unlink_blkio_group(void *key, struct blkio_group *blkg)
spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}
static struct elevator_type iosched_cfq;
static bool cfq_clear_queue(struct request_queue *q)
{
lockdep_assert_held(q->queue_lock);
/* shoot down blkgs iff the current elevator is cfq */
if (!q->elevator || q->elevator->type != &iosched_cfq)
return true;
return cfq_release_cfq_groups(q->elevator->elevator_data);
}
#else /* GROUP_IOSCHED */
static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd)
{
@ -3875,6 +3892,7 @@ static struct elevator_type iosched_cfq = {
static struct blkio_policy_type blkio_policy_cfq = {
.ops = {
.blkio_unlink_group_fn = cfq_unlink_blkio_group,
.blkio_clear_queue_fn = cfq_clear_queue,
.blkio_update_group_weight_fn = cfq_update_blkio_group_weight,
},
.plid = BLKIO_POLICY_PROP,

View File

@ -38,6 +38,7 @@
#include <trace/events/block.h>
#include "blk.h"
#include "blk-cgroup.h"
static DEFINE_SPINLOCK(elv_list_lock);
static LIST_HEAD(elv_list);
@ -894,6 +895,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
ioc_clear_queue(q);
spin_unlock_irq(q->queue_lock);
blkg_destroy_all(q);
/* allocate, init and register new elevator */
err = -ENOMEM;
q->elevator = elevator_alloc(q, new_e);