Merge tag 'cgroup-for-6.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup updates from Tejun Heo:

 - cpuset now support isolated cpus.partition type, which will enable
   dynamic CPU isolation

 - pids.peak added to remember the max number of pids used

 - holes in cgroup namespace plugged

 - internal cleanups

* tag 'cgroup-for-6.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup: (25 commits)
  cgroup: use strscpy() is more robust and safer
  iocost_monitor: reorder BlkgIterator
  cgroup: simplify code in cgroup_apply_control
  cgroup: Make cgroup_get_from_id() prettier
  cgroup/cpuset: remove unreachable code
  cgroup: Remove CFTYPE_PRESSURE
  cgroup: Improve cftype add/rm error handling
  kselftest/cgroup: Add cpuset v2 partition root state test
  cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst
  cgroup/cpuset: Make partition invalid if cpumask change violates exclusivity rule
  cgroup/cpuset: Relocate a code block in validate_change()
  cgroup/cpuset: Show invalid partition reason string
  cgroup/cpuset: Add a new isolated cpus.partition type
  cgroup/cpuset: Relax constraints to partition & cpus changes
  cgroup/cpuset: Allow no-task partition to have empty cpuset.cpus.effective
  cgroup/cpuset: Miscellaneous cleanups & add helper functions
  cgroup/cpuset: Enable update_tasks_cpumask() on top_cpuset
  cgroup: add pids.peak interface for pids controller
  cgroup: Remove data-race around cgrp_dfl_visible
  cgroup: Fix build failure when CONFIG_SHRINKER_DEBUG
  ...

Author: torvalds

Documentation/admin-guide/cgroup-v2.rst

@@ -2190,75 +2190,93 @@ Cpuset Interface Files
 
 	It accepts only the following input values when written to.
 
-	  ========	================================
-	  "root"	a partition root
-	  "member"	a non-root member of a partition
-	  ========	================================
-
-	When set to be a partition root, the current cgroup is the
-	root of a new partition or scheduling domain that comprises
-	itself and all its descendants except those that are separate
-	partition roots themselves and their descendants.  The root
-	cgroup is always a partition root.
-
-	There are constraints on where a partition root can be set.
-	It can only be set in a cgroup if all the following conditions
-	are true.
-
-	1) The "cpuset.cpus" is not empty and the list of CPUs are
-	   exclusive, i.e. they are not shared by any of its siblings.
-	2) The parent cgroup is a partition root.
-	3) The "cpuset.cpus" is also a proper subset of the parent's
-	   "cpuset.cpus.effective".
-	4) There is no child cgroups with cpuset enabled.  This is for
-	   eliminating corner cases that have to be handled if such a
-	   condition is allowed.
-
-	Setting it to partition root will take the CPUs away from the
-	effective CPUs of the parent cgroup.  Once it is set, this
-	file cannot be reverted back to "member" if there are any child
-	cgroups with cpuset enabled.
-
-	A parent partition cannot distribute all its CPUs to its
-	child partitions.  There must be at least one cpu left in the
-	parent partition.
-
-	Once becoming a partition root, changes to "cpuset.cpus" is
-	generally allowed as long as the first condition above is true,
-	the change will not take away all the CPUs from the parent
-	partition and the new "cpuset.cpus" value is a superset of its
-	children's "cpuset.cpus" values.
-
-	Sometimes, external factors like changes to ancestors'
-	"cpuset.cpus" or cpu hotplug can cause the state of the partition
-	root to change.  On read, the "cpuset.sched.partition" file
-	can show the following values.
-
-	  ==============	==============================
-	  "member"		Non-root member of a partition
-	  "root"		Partition root
-	  "root invalid"	Invalid partition root
-	  ==============	==============================
-
-	It is a partition root if the first 2 partition root conditions
-	above are true and at least one CPU from "cpuset.cpus" is
-	granted by the parent cgroup.
-
-	A partition root can become invalid if none of CPUs requested
-	in "cpuset.cpus" can be granted by the parent cgroup or the
-	parent cgroup is no longer a partition root itself.  In this
-	case, it is not a real partition even though the restriction
-	of the first partition root condition above will still apply.
-	The cpu affinity of all the tasks in the cgroup will then be
-	associated with CPUs in the nearest ancestor partition.
-
-	An invalid partition root can be transitioned back to a
-	real partition root if at least one of the requested CPUs
-	can now be granted by its parent.  In this case, the cpu
-	affinity of all the tasks in the formerly invalid partition
-	will be associated to the CPUs of the newly formed partition.
-	Changing the partition state of an invalid partition root to
-	"member" is always allowed even if child cpusets are present.
+	  ==========	=====================================
+	  "member"	Non-root member of a partition
+	  "root"	Partition root
+	  "isolated"	Partition root without load balancing
+	  ==========	=====================================
+
+	The root cgroup is always a partition root and its state
+	cannot be changed.  All other non-root cgroups start out as
+	"member".
+
+	When set to "root", the current cgroup is the root of a new
+	partition or scheduling domain that comprises itself and all
+	its descendants except those that are separate partition roots
+	themselves and their descendants.
+
+	When set to "isolated", the CPUs in that partition root will
+	be in an isolated state without any load balancing from the
+	scheduler.  Tasks placed in such a partition with multiple
+	CPUs should be carefully distributed and bound to each of the
+	individual CPUs for optimal performance.
+
+	The value shown in "cpuset.cpus.effective" of a partition root
+	is the CPUs that the partition root can dedicate to a potential
+	new child partition root. The new child subtracts available
+	CPUs from its parent "cpuset.cpus.effective".
+
+	A partition root ("root" or "isolated") can be in one of the
+	two possible states - valid or invalid.  An invalid partition
+	root is in a degraded state where some state information may
+	be retained, but behaves more like a "member".
+
+	All possible state transitions among "member", "root" and
+	"isolated" are allowed.
+
+	On read, the "cpuset.cpus.partition" file can show the following
+	values.
+
+	  =============================	=====================================
+	  "member"			Non-root member of a partition
+	  "root"			Partition root
+	  "isolated"			Partition root without load balancing
+	  "root invalid (<reason>)"	Invalid partition root
+	  "isolated invalid (<reason>)"	Invalid isolated partition root
+	  =============================	=====================================
+
+	In the case of an invalid partition root, a descriptive string on
+	why the partition is invalid is included within parentheses.
+
+	For a partition root to become valid, the following conditions
+	must be met.
+
+	1) The "cpuset.cpus" is exclusive with its siblings , i.e. they
+	   are not shared by any of its siblings (exclusivity rule).
+	2) The parent cgroup is a valid partition root.
+	3) The "cpuset.cpus" is not empty and must contain at least
+	   one of the CPUs from parent's "cpuset.cpus", i.e. they overlap.
+	4) The "cpuset.cpus.effective" cannot be empty unless there is
+	   no task associated with this partition.
+
+	External events like hotplug or changes to "cpuset.cpus" can
+	cause a valid partition root to become invalid and vice versa.
+	Note that a task cannot be moved to a cgroup with empty
+	"cpuset.cpus.effective".
+
+	For a valid partition root with the sibling cpu exclusivity
+	rule enabled, changes made to "cpuset.cpus" that violate the
+	exclusivity rule will invalidate the partition as well as its
+	sibiling partitions with conflicting cpuset.cpus values. So
+	care must be taking in changing "cpuset.cpus".
+
+	A valid non-root parent partition may distribute out all its CPUs
+	to its child partitions when there is no task associated with it.
+
+	Care must be taken to change a valid partition root to
+	"member" as all its child partitions, if present, will become
+	invalid causing disruption to tasks running in those child
+	partitions. These inactivated partitions could be recovered if
+	their parent is switched back to a partition root with a proper
+	set of "cpuset.cpus".
+
+	Poll and inotify events are triggered whenever the state of
+	"cpuset.cpus.partition" changes.  That includes changes caused
+	by write to "cpuset.cpus.partition", cpu hotplug or other
+	changes that modify the validity status of the partition.
+	This will allow user space agents to monitor unexpected changes
+	to "cpuset.cpus.partition" without the need to do continuous
+	polling.
 
 
 Device controller

block/blk-cgroup-fc-appid.c

@@ -19,8 +19,8 @@ int blkcg_set_fc_appid(char *app_id, u64 cgrp_id, size_t app_id_len)
 		return -EINVAL;
 
 	cgrp = cgroup_get_from_id(cgrp_id);
-	if (!cgrp)
-		return -ENOENT;
+	if (IS_ERR(cgrp))
+		return PTR_ERR(cgrp);
 	css = cgroup_get_e_css(cgrp, &io_cgrp_subsys);
 	if (!css) {
 		ret = -ENOENT;

include/linux/cgroup-defs.h

@@ -126,11 +126,11 @@ enum {
 	CFTYPE_NO_PREFIX	= (1 << 3),	/* (DON'T USE FOR NEW FILES) no subsys prefix */
 	CFTYPE_WORLD_WRITABLE	= (1 << 4),	/* (DON'T USE FOR NEW FILES) S_IWUGO */
 	CFTYPE_DEBUG		= (1 << 5),	/* create when cgroup_debug */
-	CFTYPE_PRESSURE		= (1 << 6),	/* only if pressure feature is enabled */
 
 	/* internal flags, do not use outside cgroup core proper */
 	__CFTYPE_ONLY_ON_DFL	= (1 << 16),	/* only on default hierarchy */
 	__CFTYPE_NOT_ON_DFL	= (1 << 17),	/* not on default hierarchy */
+	__CFTYPE_ADDED		= (1 << 18),
 };
 
 /*
@@ -384,7 +384,7 @@ struct cgroup {
 	/*
 	 * The depth this cgroup is at.  The root is at depth zero and each
 	 * step down the hierarchy increments the level.  This along with
-	 * ancestor_ids[] can determine whether a given cgroup is a
+	 * ancestors[] can determine whether a given cgroup is a
 	 * descendant of another without traversing the hierarchy.
 	 */
 	int level;
@@ -504,8 +504,8 @@ struct cgroup {
 	/* Used to store internal freezer state */
 	struct cgroup_freezer_state freezer;
 
-	/* ids of the ancestors at each level including self */
-	u64 ancestor_ids[];
+	/* All ancestors including self */
+	struct cgroup *ancestors[];
 };
 
 /*
@@ -522,11 +522,15 @@ struct cgroup_root {
 	/* Unique id for this hierarchy. */
 	int hierarchy_id;
 
-	/* The root cgroup.  Root is destroyed on its release. */
+	/*
+	 * The root cgroup. The containing cgroup_root will be destroyed on its
+	 * release. cgrp->ancestors[0] will be used overflowing into the
+	 * following field. cgrp_ancestor_storage must immediately follow.
+	 */
 	struct cgroup cgrp;
 
-	/* for cgrp->ancestor_ids[0] */
-	u64 cgrp_ancestor_id_storage;
+	/* must follow cgrp for cgrp->ancestors[0], see above */
+	struct cgroup *cgrp_ancestor_storage;
 
 	/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
 	atomic_t nr_cgrps;

include/linux/cgroup.h

@@ -575,7 +575,7 @@ static inline bool cgroup_is_descendant(struct cgroup *cgrp,
 {
 	if (cgrp->root != ancestor->root || cgrp->level < ancestor->level)
 		return false;
-	return cgrp->ancestor_ids[ancestor->level] == cgroup_id(ancestor);
+	return cgrp->ancestors[ancestor->level] == ancestor;
 }
 
 /**
@@ -592,11 +592,9 @@ static inline bool cgroup_is_descendant(struct cgroup *cgrp,
 static inline struct cgroup *cgroup_ancestor(struct cgroup *cgrp,
 					     int ancestor_level)
 {
-	if (cgrp->level < ancestor_level)
+	if (ancestor_level < 0 || ancestor_level > cgrp->level)
 		return NULL;
-	while (cgrp && cgrp->level > ancestor_level)
-		cgrp = cgroup_parent(cgrp);
-	return cgrp;
+	return cgrp->ancestors[ancestor_level];
 }
 
 /**
@@ -748,11 +746,6 @@ static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
 
 static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
 {}
-
-static inline struct cgroup *cgroup_get_from_id(u64 id)
-{
-	return NULL;
-}
 #endif /* !CONFIG_CGROUPS */
 
 #ifdef CONFIG_CGROUPS

kernel/cgroup/cgroup-internal.h

@@ -250,6 +250,8 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
 
 int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
 		       bool threadgroup);
+void cgroup_attach_lock(bool lock_threadgroup);
+void cgroup_attach_unlock(bool lock_threadgroup);
 struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup,
 					     bool *locked)
 	__acquires(&cgroup_threadgroup_rwsem);

kernel/cgroup/cgroup-v1.c

@@ -59,8 +59,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 	int retval = 0;
 
 	mutex_lock(&cgroup_mutex);
-	cpus_read_lock();
-	percpu_down_write(&cgroup_threadgroup_rwsem);
+	cgroup_attach_lock(true);
 	for_each_root(root) {
 		struct cgroup *from_cgrp;
 
@@ -72,8 +71,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 		if (retval)
 			break;
 	}
-	percpu_up_write(&cgroup_threadgroup_rwsem);
-	cpus_read_unlock();
+	cgroup_attach_unlock(true);
 	mutex_unlock(&cgroup_mutex);
 
 	return retval;