Commit 4c70fb26 authored by Chen Ridong's avatar Chen Ridong Committed by Tejun Heo
Browse files

cpuset: remove redundant CS_ONLINE flag 



The CS_ONLINE flag was introduced prior to the CSS_ONLINE flag in the
cpuset subsystem. Currently, the flag setting sequence is as follows:

1. cpuset_css_online() sets CS_ONLINE
2. css->flags gets CSS_ONLINE set
...
3. cgroup->kill_css sets CSS_DYING
4. cpuset_css_offline() clears CS_ONLINE
5. css->flags clears CSS_ONLINE

The is_cpuset_online() check currently occurs between steps 1 and 3.
However, it would be equally safe to perform this check between steps 2
and 3, as CSS_ONLINE provides the same synchronization guarantee as
CS_ONLINE.

Since CS_ONLINE is redundant with CSS_ONLINE and provides no additional
synchronization benefits, we can safely remove it to simplify the code.

Signed-off-by: default avatarChen Ridong <chenridong@huawei.com>
Acked-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 8a013ec9

include/linux/cgroup.h

+5 −0
Original line number Diff line number Diff line
@@ -354,6 +354,11 @@ static inline bool css_is_dying(struct cgroup_subsys_state *css) 
	return css->flags & CSS_DYING;

}



static inline bool css_is_online(struct cgroup_subsys_state *css)

{

	return css->flags & CSS_ONLINE;

}



static inline bool css_is_self(struct cgroup_subsys_state *css)

{

	if (css == &css->cgroup->self) {

kernel/cgroup/cpuset-internal.h

+1 −2
Original line number Diff line number Diff line
@@ -38,7 +38,6 @@ enum prs_errcode { 


/* bits in struct cpuset flags field */

typedef enum {

	CS_ONLINE,

	CS_CPU_EXCLUSIVE,

	CS_MEM_EXCLUSIVE,

	CS_MEM_HARDWALL,
@@ -202,7 +201,7 @@ static inline struct cpuset *parent_cs(struct cpuset *cs) 
/* convenient tests for these bits */

static inline bool is_cpuset_online(struct cpuset *cs)

{

	return test_bit(CS_ONLINE, &cs->flags) && !css_is_dying(&cs->css);

	return css_is_online(&cs->css) && !css_is_dying(&cs->css);

}



static inline int is_cpu_exclusive(const struct cpuset *cs)

kernel/cgroup/cpuset.c

+1 −3
Original line number Diff line number Diff line
@@ -207,7 +207,7 @@ static inline void notify_partition_change(struct cpuset *cs, int old_prs) 
 * parallel, we may leave an offline CPU in cpu_allowed or some other masks.

 */

static struct cpuset top_cpuset = {

	.flags = BIT(CS_ONLINE) | BIT(CS_CPU_EXCLUSIVE) |

	.flags = BIT(CS_CPU_EXCLUSIVE) |

		 BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE),

	.partition_root_state = PRS_ROOT,

	.relax_domain_level = -1,
@@ -3496,7 +3496,6 @@ static int cpuset_css_online(struct cgroup_subsys_state *css) 
	cpus_read_lock();

	mutex_lock(&cpuset_mutex);



	set_bit(CS_ONLINE, &cs->flags);

	if (is_spread_page(parent))

		set_bit(CS_SPREAD_PAGE, &cs->flags);

	if (is_spread_slab(parent))
@@ -3571,7 +3570,6 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css) 
		cpuset_update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);



	cpuset_dec();

	clear_bit(CS_ONLINE, &cs->flags);



	mutex_unlock(&cpuset_mutex);

	cpus_read_unlock();