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Subject[PATCH 17/36] blkcg: kill the mind-bending blkg->dev
Date
blkg->dev is dev_t recording the device number of the block device for
the associated request_queue. It is used to identify the associated
block device when printing out configuration or stats.

This is redundant to begin with. A blkg is an association between a
cgroup and a request_queue and it of course is possible to reach
request_queue from blkg and synchronization conventions are in place
for safe q dereferencing, so this shouldn't be necessary from the
beginning. Furthermore, it's initialized by sscanf()ing the device
name of backing_dev_info. The mind boggles.

Anyways, if blkg is visible under rcu lock, we *know* that the
associated request_queue hasn't gone away yet and its bdi is
registered and alive - blkg can't be created for request_queue which
hasn't been fully initialized and it can't go away before blkg is
removed.

Let stat and conf read functions get device name from
blkg->q->backing_dev_info.dev and pass it down to printing functions
and remove blkg->dev.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
---
block/blk-cgroup.c | 86 ++++++++++++++++++++++++++------------------------
block/blk-cgroup.h | 2 -
block/blk-throttle.c | 51 +----------------------------
block/cfq-iosched.c | 21 ------------
4 files changed, 47 insertions(+), 113 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index adf61c9..8742af3 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -662,10 +662,10 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
return 0;
}

-static void blkio_get_key_name(enum stat_sub_type type, dev_t dev, char *str,
- int chars_left, bool diskname_only)
+static void blkio_get_key_name(enum stat_sub_type type, const char *dname,
+ char *str, int chars_left, bool diskname_only)
{
- snprintf(str, chars_left, "%d:%d", MAJOR(dev), MINOR(dev));
+ snprintf(str, chars_left, "%s", dname);
chars_left -= strlen(str);
if (chars_left <= 0) {
printk(KERN_WARNING
@@ -696,9 +696,9 @@ static void blkio_get_key_name(enum stat_sub_type type, dev_t dev, char *str,
}

static uint64_t blkio_fill_stat(char *str, int chars_left, uint64_t val,
- struct cgroup_map_cb *cb, dev_t dev)
+ struct cgroup_map_cb *cb, const char *dname)
{
- blkio_get_key_name(0, dev, str, chars_left, true);
+ blkio_get_key_name(0, dname, str, chars_left, true);
cb->fill(cb, str, val);
return val;
}
@@ -730,7 +730,8 @@ static uint64_t blkio_read_stat_cpu(struct blkio_group *blkg,
}

static uint64_t blkio_get_stat_cpu(struct blkio_group *blkg,
- struct cgroup_map_cb *cb, dev_t dev, enum stat_type_cpu type)
+ struct cgroup_map_cb *cb, const char *dname,
+ enum stat_type_cpu type)
{
uint64_t disk_total, val;
char key_str[MAX_KEY_LEN];
@@ -738,12 +739,14 @@ static uint64_t blkio_get_stat_cpu(struct blkio_group *blkg,

if (type == BLKIO_STAT_CPU_SECTORS) {
val = blkio_read_stat_cpu(blkg, type, 0);
- return blkio_fill_stat(key_str, MAX_KEY_LEN - 1, val, cb, dev);
+ return blkio_fill_stat(key_str, MAX_KEY_LEN - 1, val, cb,
+ dname);
}

for (sub_type = BLKIO_STAT_READ; sub_type < BLKIO_STAT_TOTAL;
sub_type++) {
- blkio_get_key_name(sub_type, dev, key_str, MAX_KEY_LEN, false);
+ blkio_get_key_name(sub_type, dname, key_str, MAX_KEY_LEN,
+ false);
val = blkio_read_stat_cpu(blkg, type, sub_type);
cb->fill(cb, key_str, val);
}
@@ -751,14 +754,16 @@ static uint64_t blkio_get_stat_cpu(struct blkio_group *blkg,
disk_total = blkio_read_stat_cpu(blkg, type, BLKIO_STAT_READ) +
blkio_read_stat_cpu(blkg, type, BLKIO_STAT_WRITE);

- blkio_get_key_name(BLKIO_STAT_TOTAL, dev, key_str, MAX_KEY_LEN, false);
+ blkio_get_key_name(BLKIO_STAT_TOTAL, dname, key_str, MAX_KEY_LEN,
+ false);
cb->fill(cb, key_str, disk_total);
return disk_total;
}

/* This should be called with blkg->stats_lock held */
static uint64_t blkio_get_stat(struct blkio_group *blkg,
- struct cgroup_map_cb *cb, dev_t dev, enum stat_type type)
+ struct cgroup_map_cb *cb, const char *dname,
+ enum stat_type type)
{
uint64_t disk_total;
char key_str[MAX_KEY_LEN];
@@ -766,11 +771,11 @@ static uint64_t blkio_get_stat(struct blkio_group *blkg,

if (type == BLKIO_STAT_TIME)
return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
- blkg->stats.time, cb, dev);
+ blkg->stats.time, cb, dname);
#ifdef CONFIG_DEBUG_BLK_CGROUP
if (type == BLKIO_STAT_UNACCOUNTED_TIME)
return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
- blkg->stats.unaccounted_time, cb, dev);
+ blkg->stats.unaccounted_time, cb, dname);
if (type == BLKIO_STAT_AVG_QUEUE_SIZE) {
uint64_t sum = blkg->stats.avg_queue_size_sum;
uint64_t samples = blkg->stats.avg_queue_size_samples;
@@ -778,30 +783,33 @@ static uint64_t blkio_get_stat(struct blkio_group *blkg,
do_div(sum, samples);
else
sum = 0;
- return blkio_fill_stat(key_str, MAX_KEY_LEN - 1, sum, cb, dev);
+ return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
+ sum, cb, dname);
}
if (type == BLKIO_STAT_GROUP_WAIT_TIME)
return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
- blkg->stats.group_wait_time, cb, dev);
+ blkg->stats.group_wait_time, cb, dname);
if (type == BLKIO_STAT_IDLE_TIME)
return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
- blkg->stats.idle_time, cb, dev);
+ blkg->stats.idle_time, cb, dname);
if (type == BLKIO_STAT_EMPTY_TIME)
return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
- blkg->stats.empty_time, cb, dev);
+ blkg->stats.empty_time, cb, dname);
if (type == BLKIO_STAT_DEQUEUE)
return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
- blkg->stats.dequeue, cb, dev);
+ blkg->stats.dequeue, cb, dname);
#endif

for (sub_type = BLKIO_STAT_READ; sub_type < BLKIO_STAT_TOTAL;
sub_type++) {
- blkio_get_key_name(sub_type, dev, key_str, MAX_KEY_LEN, false);
+ blkio_get_key_name(sub_type, dname, key_str, MAX_KEY_LEN,
+ false);
cb->fill(cb, key_str, blkg->stats.stat_arr[type][sub_type]);
}
disk_total = blkg->stats.stat_arr[type][BLKIO_STAT_READ] +
blkg->stats.stat_arr[type][BLKIO_STAT_WRITE];
- blkio_get_key_name(BLKIO_STAT_TOTAL, dev, key_str, MAX_KEY_LEN, false);
+ blkio_get_key_name(BLKIO_STAT_TOTAL, dname, key_str, MAX_KEY_LEN,
+ false);
cb->fill(cb, key_str, disk_total);
return disk_total;
}
@@ -946,14 +954,15 @@ static int blkiocg_file_write(struct cgroup *cgrp, struct cftype *cft,
static void blkio_print_group_conf(struct cftype *cft, struct blkio_group *blkg,
struct seq_file *m)
{
+ const char *dname = dev_name(blkg->q->backing_dev_info.dev);
int fileid = BLKIOFILE_ATTR(cft->private);
int rw = WRITE;

switch (blkg->plid) {
case BLKIO_POLICY_PROP:
if (blkg->conf.weight)
- seq_printf(m, "%u:%u\t%u\n", MAJOR(blkg->dev),
- MINOR(blkg->dev), blkg->conf.weight);
+ seq_printf(m, "%s\t%u\n",
+ dname, blkg->conf.weight);
break;
case BLKIO_POLICY_THROTL:
switch (fileid) {
@@ -961,19 +970,15 @@ static void blkio_print_group_conf(struct cftype *cft, struct blkio_group *blkg,
rw = READ;
case BLKIO_THROTL_write_bps_device:
if (blkg->conf.bps[rw])
- seq_printf(m, "%u:%u\t%llu\n",
- MAJOR(blkg->dev),
- MINOR(blkg->dev),
- blkg->conf.bps[rw]);
+ seq_printf(m, "%s\t%llu\n",
+ dname, blkg->conf.bps[rw]);
break;
case BLKIO_THROTL_read_iops_device:
rw = READ;
case BLKIO_THROTL_write_iops_device:
if (blkg->conf.iops[rw])
- seq_printf(m, "%u:%u\t%u\n",
- MAJOR(blkg->dev),
- MINOR(blkg->dev),
- blkg->conf.iops[rw]);
+ seq_printf(m, "%s\t%u\n",
+ dname, blkg->conf.iops[rw]);
break;
}
break;
@@ -1044,18 +1049,17 @@ static int blkio_read_blkg_stats(struct blkio_cgroup *blkcg,

rcu_read_lock();
hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) {
- if (blkg->dev) {
- if (BLKIOFILE_POLICY(cft->private) != blkg->plid)
- continue;
- if (pcpu)
- cgroup_total += blkio_get_stat_cpu(blkg, cb,
- blkg->dev, type);
- else {
- spin_lock_irq(&blkg->stats_lock);
- cgroup_total += blkio_get_stat(blkg, cb,
- blkg->dev, type);
- spin_unlock_irq(&blkg->stats_lock);
- }
+ const char *dname = dev_name(blkg->q->backing_dev_info.dev);
+
+ if (BLKIOFILE_POLICY(cft->private) != blkg->plid)
+ continue;
+ if (pcpu)
+ cgroup_total += blkio_get_stat_cpu(blkg, cb, dname,
+ type);
+ else {
+ spin_lock_irq(&blkg->stats_lock);
+ cgroup_total += blkio_get_stat(blkg, cb, dname, type);
+ spin_unlock_irq(&blkg->stats_lock);
}
}
if (show_total)
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 9a5c68d..7ebecf6 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -166,8 +166,6 @@ struct blkio_group {
unsigned short blkcg_id;
/* Store cgroup path */
char path[128];
- /* The device MKDEV(major, minor), this group has been created for */
- dev_t dev;
/* policy which owns this blk group */
enum blkio_policy_id plid;

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 791b107..52a4293 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -212,50 +212,12 @@ static struct blkio_group *throtl_alloc_blkio_group(struct request_queue *q,
return &tg->blkg;
}

-static void
-__throtl_tg_fill_dev_details(struct throtl_data *td, struct throtl_grp *tg)
-{
- struct backing_dev_info *bdi = &td->queue->backing_dev_info;
- unsigned int major, minor;
-
- if (!tg || tg->blkg.dev)
- return;
-
- /*
- * Fill in device details for a group which might not have been
- * filled at group creation time as queue was being instantiated
- * and driver had not attached a device yet
- */
- if (bdi->dev && dev_name(bdi->dev)) {
- sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
- tg->blkg.dev = MKDEV(major, minor);
- }
-}
-
-/*
- * Should be called with without queue lock held. Here queue lock will be
- * taken rarely. It will be taken only once during life time of a group
- * if need be
- */
-static void
-throtl_tg_fill_dev_details(struct throtl_data *td, struct throtl_grp *tg)
-{
- if (!tg || tg->blkg.dev)
- return;
-
- spin_lock_irq(td->queue->queue_lock);
- __throtl_tg_fill_dev_details(td, tg);
- spin_unlock_irq(td->queue->queue_lock);
-}
-
static void throtl_link_blkio_group(struct request_queue *q,
struct blkio_group *blkg)
{
struct throtl_data *td = q->td;
struct throtl_grp *tg = tg_of_blkg(blkg);

- __throtl_tg_fill_dev_details(td, tg);
-
hlist_add_head(&tg->tg_node, &td->tg_list);
td->nr_undestroyed_grps++;
}
@@ -263,20 +225,14 @@ static void throtl_link_blkio_group(struct request_queue *q,
static struct
throtl_grp *throtl_lookup_tg(struct throtl_data *td, struct blkio_cgroup *blkcg)
{
- struct throtl_grp *tg = NULL;
-
/*
* This is the common case when there are no blkio cgroups.
* Avoid lookup in this case
*/
if (blkcg == &blkio_root_cgroup)
- tg = td->root_tg;
- else
- tg = tg_of_blkg(blkg_lookup(blkcg, td->queue,
- BLKIO_POLICY_THROTL));
+ return td->root_tg;

- __throtl_tg_fill_dev_details(td, tg);
- return tg;
+ return tg_of_blkg(blkg_lookup(blkcg, td->queue, BLKIO_POLICY_THROTL));
}

static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
@@ -303,7 +259,6 @@ static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
tg = td->root_tg;
}

- __throtl_tg_fill_dev_details(td, tg);
return tg;
}

@@ -1090,8 +1045,6 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
blkcg = task_blkio_cgroup(current);
tg = throtl_lookup_tg(td, blkcg);
if (tg) {
- throtl_tg_fill_dev_details(td, tg);
-
if (tg_no_rule_group(tg, rw)) {
blkiocg_update_dispatch_stats(&tg->blkg, bio->bi_size,
rw, rw_is_sync(bio->bi_rw));
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 08d4fdd..f67d109 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1052,20 +1052,7 @@ static void cfq_link_blkio_group(struct request_queue *q,
struct blkio_group *blkg)
{
struct cfq_data *cfqd = q->elevator->elevator_data;
- struct backing_dev_info *bdi = &q->backing_dev_info;
struct cfq_group *cfqg = cfqg_of_blkg(blkg);
- unsigned int major, minor;
-
- /*
- * Add group onto cgroup list. It might happen that bdi->dev is
- * not initialized yet. Initialize this new group without major
- * and minor info and this info will be filled in once a new thread
- * comes for IO.
- */
- if (bdi->dev) {
- sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
- blkg->dev = MKDEV(major, minor);
- }

cfqd->nr_blkcg_linked_grps++;

@@ -1104,7 +1091,6 @@ static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,
struct blkio_cgroup *blkcg)
{
struct request_queue *q = cfqd->queue;
- struct backing_dev_info *bdi = &q->backing_dev_info;
struct cfq_group *cfqg = NULL;

/* avoid lookup for the common case where there's no blkio cgroup */
@@ -1118,13 +1104,6 @@ static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,
cfqg = cfqg_of_blkg(blkg);
}

- if (cfqg && !cfqg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
- unsigned int major, minor;
-
- sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
- cfqg->blkg.dev = MKDEV(major, minor);
- }
-
return cfqg;
}

--
1.7.7.3


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