Hi,
I noticed two different behaviours, the second one looks weird for me:
1) when the cgroup is manually created:
mkdir /cgroup/foo
echo $$ > /cgroup/foo/tasks
only the "attach" callback is called as expected.
2) when the cgroup is automatically created via the ns_cgroup with the
clone function and the namespace flags,
the "attach" *and* the "fork" callbacks are called.
IMHO, these two different behaviours look inconsistent. Won't this lead
to some problems or a specific code to handle both cases if a cgroup is
using the fork and the attach hooks ?
For example, let's imagine we create a control group which shows the
number of tasks running. We have a global atomic and we display its
value in the cgroupfs.
When a task attaches to the cgroup, we do atomic_inc in the attach
callback. For all its child, the fork hook will do atomic_inc and exit
hook will do atomic_dec.
If we create the cgroup manually like the case 1) that works. But if we
use the control group with the ns_cgroup the task counter will be set to
2 for the first tasks entering the cgroup because the attach callback
will increment the counter and the fork callback will increment it again.
In attachment a source code to illustrate the example.
Shouldn't the ns_cgroup_clone be called after the cgroup_fork_callbacks
in copy_process function ? So we don't call the fork callback for the
first tasks and we keep the consistency ?
Thanks
-- Daniel
---
include/linux/cgroup_subsys.h | 1
kernel/Makefile | 2
kernel/cgroup_bug.c | 87 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 89 insertions(+), 1 deletion(-)
Index: linux-2.6/kernel/cgroup_bug.c
===================================================================
--- /dev/null
+++ linux-2.6/kernel/cgroup_bug.c
@@ -0,0 +1,87 @@
+#include <linux/cgroup.h>
+#include <asm/atomic.h>
+
+struct bug_cg {
+ struct cgroup_subsys_state css;
+ atomic_t ntasks;
+};
+
+static inline struct bug_cg *bug_cgroup(struct cgroup *cgroup)
+{
+ return container_of(cgroup_subsys_state(cgroup, bug_subsys_id),
+ struct bug_cg, css);
+}
+
+static struct cgroup_subsys_state *bug_cgroup_create(struct cgroup_subsys *ss,
+ struct cgroup *cgroup)
+{
+ struct bug_cg *bug_cg;
+
+ bug_cg = kzalloc(sizeof(*bug_cg), GFP_KERNEL);
+ if (!bug_cg)
+ return ERR_PTR(-ENOMEM);
+
+ atomic_set(&bug_cg->ntasks, 0);
+
+ return &bug_cg->css;
+}
+
+static void bug_cgroup_destroy(struct cgroup_subsys *ss, struct cgroup *cgroup)
+{
+ struct bug_cg *bug_cg = bug_cgroup(cgroup);
+ kfree(bug_cg);
+}
+
+static void bug_cgroup_attach(struct cgroup_subsys *ss, struct cgroup *cgroup,
+ struct cgroup *old_cgroup,
+ struct task_struct *task)
+{
+ struct bug_cg *bug_cg = bug_cgroup(cgroup);
+
+ atomic_inc(&bug_cg->ntasks);
+}
+
+static int bug_cgroup_fork(struct cgroup_subsys *ss, struct task_struct *task,
+ unsigned long clone_flags)
+{
+ struct cgroup *cgroup = task_cgroup(task, bug_subsys_id);
+
+ atomic_inc(&bug_cgroup(cgroup)->ntasks);
+
+ return 0;
+}
+
+static void bug_cgroup_exit(struct cgroup_subsys *ss, struct task_struct *task)
+{
+ struct cgroup *cgroup = task_cgroup(task, bug_subsys_id);
+
+ atomic_dec(&bug_cgroup(cgroup)->ntasks);
+}
+
+static u64 task_count_read(struct cgroup *cgroup, struct cftype *cft)
+{
+ return atomic_read(&bug_cgroup(cgroup)->ntasks);
+}
+
+static struct cftype files[] = {
+ {
+ .name = "ntask",
+ .read_u64 = task_count_read,
+ },
+};
+
+static int bug_cgroup_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
+{
+ return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
+}
+
+struct cgroup_subsys bug_subsys = {
+ .name = "bug",
+ .subsys_id = bug_subsys_id,
+ .create = bug_cgroup_create,
+ .destroy = bug_cgroup_destroy,
+ .populate = bug_cgroup_populate,
+ .attach = bug_cgroup_attach,
+ .fork = bug_cgroup_fork,
+ .exit = bug_cgroup_exit,
+};
Index: linux-2.6/include/linux/cgroup_subsys.h
===================================================================
--- linux-2.6.orig/include/linux/cgroup_subsys.h
+++ linux-2.6/include/linux/cgroup_subsys.h
@@ -21,6 +21,7 @@ SUBSYS(debug)
#ifdef CONFIG_CGROUP_NS
SUBSYS(ns)
+SUBSYS(bug)
#endif
/* */
Index: linux-2.6/kernel/Makefile
===================================================================
--- linux-2.6.orig/kernel/Makefile
+++ linux-2.6/kernel/Makefile
@@ -60,7 +60,7 @@ obj-$(CONFIG_CGROUPS) += cgroup.o
obj-$(CONFIG_CGROUP_DEBUG) += cgroup_debug.o
obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o
obj-$(CONFIG_CPUSETS) += cpuset.o
-obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o
+obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o cgroup_bug.o
obj-$(CONFIG_UTS_NS) += utsname.o
obj-$(CONFIG_USER_NS) += user_namespace.o
obj-$(CONFIG_PID_NS) += pid_namespace.o
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