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Subject[PATCH 10/16] cgroup: separate out put_css_set_locked() and remove put_css_set_taskexit()
Date
put_css_set() is performed in two steps - it first tries to put
without grabbing css_set_rwsem if such put wouldn't make the count
zero. If that fails, it puts after write-locking css_set_rwsem. This
patch separates out the second phase into put_css_set_locked() which
should be called with css_set_rwsem locked.

Also, put_css_set_taskexit() is droped and put_css_set() is made to
take @taskexit. There are only a handful users of these functions.
No point in providing different variants.

put_css_locked() will be used by later changes. This patch doesn't
introduce any functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/cgroup.c | 50 +++++++++++++++++++++++---------------------------
1 file changed, 23 insertions(+), 27 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8c1f840..63d1a4e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -369,22 +369,14 @@ static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
return key;
}

-static void __put_css_set(struct css_set *cset, int taskexit)
+static void put_css_set_locked(struct css_set *cset, bool taskexit)
{
struct cgrp_cset_link *link, *tmp_link;

- /*
- * Ensure that the refcount doesn't hit zero while any readers
- * can see it. Similar to atomic_dec_and_lock(), but for an
- * rwlock
- */
- if (atomic_add_unless(&cset->refcount, -1, 1))
- return;
- down_write(&css_set_rwsem);
- if (!atomic_dec_and_test(&cset->refcount)) {
- up_write(&css_set_rwsem);
+ lockdep_assert_held(&css_set_rwsem);
+
+ if (!atomic_dec_and_test(&cset->refcount))
return;
- }

/* This css_set is dead. unlink it and release cgroup refcounts */
hash_del(&cset->hlist);
@@ -406,10 +398,24 @@ static void __put_css_set(struct css_set *cset, int taskexit)
kfree(link);
}

- up_write(&css_set_rwsem);
kfree_rcu(cset, rcu_head);
}

+static void put_css_set(struct css_set *cset, bool taskexit)
+{
+ /*
+ * Ensure that the refcount doesn't hit zero while any readers
+ * can see it. Similar to atomic_dec_and_lock(), but for an
+ * rwlock
+ */
+ if (atomic_add_unless(&cset->refcount, -1, 1))
+ return;
+
+ down_write(&css_set_rwsem);
+ put_css_set_locked(cset, taskexit);
+ up_write(&css_set_rwsem);
+}
+
/*
* refcounted get/put for css_set objects
*/
@@ -418,16 +424,6 @@ static inline void get_css_set(struct css_set *cset)
atomic_inc(&cset->refcount);
}

-static inline void put_css_set(struct css_set *cset)
-{
- __put_css_set(cset, 0);
-}
-
-static inline void put_css_set_taskexit(struct css_set *cset)
-{
- __put_css_set(cset, 1);
-}
-
/**
* compare_css_sets - helper function for find_existing_css_set().
* @cset: candidate css_set being tested
@@ -1751,7 +1747,7 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
* we're safe to drop it here; it will be freed under RCU.
*/
set_bit(CGRP_RELEASABLE, &old_cgrp->flags);
- put_css_set(old_cset);
+ put_css_set(old_cset, false);
}

/**
@@ -1897,7 +1893,7 @@ out_put_css_set_refs:
tc = flex_array_get(group, i);
if (!tc->cset)
break;
- put_css_set(tc->cset);
+ put_css_set(tc->cset, false);
}
}
out_cancel_attach:
@@ -3714,7 +3710,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)

/*
* css_set_rwsem synchronizes access to ->cset_links and prevents
- * @cgrp from being removed while __put_css_set() is in progress.
+ * @cgrp from being removed while put_css_set() is in progress.
*/
down_read(&css_set_rwsem);
empty = list_empty(&cgrp->cset_links);
@@ -4266,7 +4262,7 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
}
task_unlock(tsk);

- put_css_set_taskexit(cset);
+ put_css_set(cset, true);
}

static void check_for_release(struct cgroup *cgrp)
--
1.8.5.3


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