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Message-ID: <20121108103928.GD31821@dhcp22.suse.cz>
Date: Thu, 8 Nov 2012 11:39:28 +0100
From: Michal Hocko <mhocko@...e.cz>
To: Tejun Heo <tj@...nel.org>
Cc: lizefan@...wei.com, rjw@...k.pl,
containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
fweisbec@...il.com
Subject: Re: [PATCH 6/9] cgroup_freezer: make freezer->state mask of flags
On Sat 03-11-12 01:38:32, Tejun Heo wrote:
> freezer->state was an enum value - one of THAWED, FREEZING and FROZEN.
> As the scheduled full hierarchy support requires more than one
> freezing condition, switch it to mask of flags. If FREEZING is not
> set, it's thawed. FREEZING is set if freezing or frozen. If frozen,
> both FREEZING and FROZEN are set. Now that tasks can be attached to
> an already frozen cgroup, this also makes freezing condition checks
> more natural.
>
> This patch doesn't introduce any behavior change.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
I think it would be nicer to use freezer_state_flags enum rather than
unsigned int for the state. I would even expect gcc to complain about
that but it looks like -fstrict-enums is c++ specific (so long enum
safety).
Anyway
Reviewed-by: Michal Hocko <mhocko@...e.cz>
> ---
> kernel/cgroup_freezer.c | 60 ++++++++++++++++++++++---------------------------
> 1 file changed, 27 insertions(+), 33 deletions(-)
>
> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> index 2690830..e76aa9f 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -22,15 +22,14 @@
> #include <linux/freezer.h>
> #include <linux/seq_file.h>
>
> -enum freezer_state {
> - CGROUP_THAWED = 0,
> - CGROUP_FREEZING,
> - CGROUP_FROZEN,
> +enum freezer_state_flags {
> + CGROUP_FREEZING = (1 << 1), /* this freezer is freezing */
> + CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */
> };
>
> struct freezer {
> struct cgroup_subsys_state css;
> - enum freezer_state state;
> + unsigned int state;
> spinlock_t lock;
> };
>
> @@ -48,12 +47,10 @@ static inline struct freezer *task_freezer(struct task_struct *task)
>
> bool cgroup_freezing(struct task_struct *task)
> {
> - enum freezer_state state;
> bool ret;
>
> rcu_read_lock();
> - state = task_freezer(task)->state;
> - ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN;
> + ret = task_freezer(task)->state & CGROUP_FREEZING;
> rcu_read_unlock();
>
> return ret;
> @@ -63,10 +60,13 @@ bool cgroup_freezing(struct task_struct *task)
> * cgroups_write_string() limits the size of freezer state strings to
> * CGROUP_LOCAL_BUFFER_SIZE
> */
> -static const char *freezer_state_strs[] = {
> - "THAWED",
> - "FREEZING",
> - "FROZEN",
> +static const char *freezer_state_strs(unsigned int state)
> +{
> + if (state & CGROUP_FROZEN)
> + return "FROZEN";
> + if (state & CGROUP_FREEZING)
> + return "FREEZING";
> + return "THAWED";
> };
>
> /*
> @@ -91,7 +91,6 @@ static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
> return ERR_PTR(-ENOMEM);
>
> spin_lock_init(&freezer->lock);
> - freezer->state = CGROUP_THAWED;
> return &freezer->css;
> }
>
> @@ -99,7 +98,7 @@ static void freezer_destroy(struct cgroup *cgroup)
> {
> struct freezer *freezer = cgroup_freezer(cgroup);
>
> - if (freezer->state != CGROUP_THAWED)
> + if (freezer->state & CGROUP_FREEZING)
> atomic_dec(&system_freezing_cnt);
> kfree(freezer);
> }
> @@ -129,15 +128,13 @@ static void freezer_attach(struct cgroup *new_cgrp, struct cgroup_taskset *tset)
> * Tasks in @tset are on @new_cgrp but may not conform to its
> * current state before executing the following - !frozen tasks may
> * be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
> - * This means that, to determine whether to freeze, one should test
> - * whether the state equals THAWED.
> */
> cgroup_taskset_for_each(task, new_cgrp, tset) {
> - if (freezer->state == CGROUP_THAWED) {
> + if (!(freezer->state & CGROUP_FREEZING)) {
> __thaw_task(task);
> } else {
> freeze_task(task);
> - freezer->state = CGROUP_FREEZING;
> + freezer->state &= ~CGROUP_FROZEN;
> }
> }
>
> @@ -159,11 +156,7 @@ static void freezer_fork(struct task_struct *task)
> goto out;
>
> spin_lock_irq(&freezer->lock);
> - /*
> - * @task might have been just migrated into a FROZEN cgroup. Test
> - * equality with THAWED. Read the comment in freezer_attach().
> - */
> - if (freezer->state != CGROUP_THAWED)
> + if (freezer->state & CGROUP_FREEZING)
> freeze_task(task);
> spin_unlock_irq(&freezer->lock);
> out:
> @@ -184,7 +177,8 @@ static void update_if_frozen(struct freezer *freezer)
> struct cgroup_iter it;
> struct task_struct *task;
>
> - if (freezer->state != CGROUP_FREEZING)
> + if (!(freezer->state & CGROUP_FREEZING) ||
> + (freezer->state & CGROUP_FROZEN))
> return;
>
> cgroup_iter_start(cgroup, &it);
> @@ -202,7 +196,7 @@ static void update_if_frozen(struct freezer *freezer)
> }
> }
>
> - freezer->state = CGROUP_FROZEN;
> + freezer->state |= CGROUP_FROZEN;
> notyet:
> cgroup_iter_end(cgroup, &it);
> }
> @@ -211,14 +205,14 @@ static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
> struct seq_file *m)
> {
> struct freezer *freezer = cgroup_freezer(cgroup);
> - enum freezer_state state;
> + unsigned int state;
>
> spin_lock_irq(&freezer->lock);
> update_if_frozen(freezer);
> state = freezer->state;
> spin_unlock_irq(&freezer->lock);
>
> - seq_puts(m, freezer_state_strs[state]);
> + seq_puts(m, freezer_state_strs(state));
> seq_putc(m, '\n');
> return 0;
> }
> @@ -258,14 +252,14 @@ static void freezer_apply_state(struct freezer *freezer, bool freeze)
> lockdep_assert_held(&freezer->lock);
>
> if (freeze) {
> - if (freezer->state == CGROUP_THAWED)
> + if (!(freezer->state & CGROUP_FREEZING))
> atomic_inc(&system_freezing_cnt);
> - freezer->state = CGROUP_FREEZING;
> + freezer->state |= CGROUP_FREEZING;
> freeze_cgroup(freezer);
> } else {
> - if (freezer->state != CGROUP_THAWED)
> + if (freezer->state & CGROUP_FREEZING)
> atomic_dec(&system_freezing_cnt);
> - freezer->state = CGROUP_THAWED;
> + freezer->state &= ~(CGROUP_FREEZING | CGROUP_FROZEN);
> unfreeze_cgroup(freezer);
> }
> }
> @@ -290,9 +284,9 @@ static int freezer_write(struct cgroup *cgroup, struct cftype *cft,
> {
> bool freeze;
>
> - if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
> + if (strcmp(buffer, freezer_state_strs(0)) == 0)
> freeze = false;
> - else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
> + else if (strcmp(buffer, freezer_state_strs(CGROUP_FROZEN)) == 0)
> freeze = true;
> else
> return -EINVAL;
> --
> 1.7.11.7
>
--
Michal Hocko
SUSE Labs
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