Commit 7f203bc8 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: Replace cgroup->ancestor_ids[] with ->ancestors[] 



Every cgroup knows all its ancestors through its ->ancestor_ids[]. There's
no advantage to remembering the IDs instead of the pointers directly and
this makes the array useless for finding an actual ancestor cgroup forcing
cgroup_ancestor() to iteratively walk up the hierarchy instead. Let's
replace cgroup->ancestor_ids[] with ->ancestors[] and remove the walking-up
from cgroup_ancestor().

While at it, improve comments around cgroup_root->cgrp_ancestor_storage.

This patch shouldn't cause user-visible behavior differences.

v2: Update cgroup_ancestor() to use ->ancestors[].

v3: cgroup_root->cgrp_ancestor_storage's type is updated to match
    cgroup->ancestors[]. Better comments.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent 568035b0

include/linux/cgroup-defs.h

+10 −6
Original line number Diff line number Diff line
@@ -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

+3 −5
Original line number Diff line number Diff line
@@ -574,7 +574,7 @@ 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;

}



/**
@@ -591,11 +591,9 @@ 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];

}



/**

kernel/cgroup/cgroup.c

+3 −4
Original line number Diff line number Diff line
@@ -2049,7 +2049,7 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask) 
	}

	root_cgrp->kn = kernfs_root_to_node(root->kf_root);

	WARN_ON_ONCE(cgroup_ino(root_cgrp) != 1);

	root_cgrp->ancestor_ids[0] = cgroup_id(root_cgrp);

	root_cgrp->ancestors[0] = root_cgrp;



	ret = css_populate_dir(&root_cgrp->self);

	if (ret)
@@ -5400,8 +5400,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name, 
	int ret;



	/* allocate the cgroup and its ID, 0 is reserved for the root */

	cgrp = kzalloc(struct_size(cgrp, ancestor_ids, (level + 1)),

		       GFP_KERNEL);

	cgrp = kzalloc(struct_size(cgrp, ancestors, (level + 1)), GFP_KERNEL);

	if (!cgrp)

		return ERR_PTR(-ENOMEM);
@@ -5453,7 +5452,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name, 


	spin_lock_irq(&css_set_lock);

	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {

		cgrp->ancestor_ids[tcgrp->level] = cgroup_id(tcgrp);

		cgrp->ancestors[tcgrp->level] = tcgrp;



		if (tcgrp != cgrp) {

			tcgrp->nr_descendants++;

net/netfilter/nft_socket.c

+5 −4
Original line number Diff line number Diff line
@@ -40,16 +40,17 @@ static noinline bool 
nft_sock_get_eval_cgroupv2(u32 *dest, struct sock *sk, const struct nft_pktinfo *pkt, u32 level)

{

	struct cgroup *cgrp;

	u64 cgid;



	if (!sk_fullsock(sk))

		return false;



	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);

	if (level > cgrp->level)

	cgrp = cgroup_ancestor(sock_cgroup_ptr(&sk->sk_cgrp_data), level);

	if (!cgrp)

		return false;



	memcpy(dest, &cgrp->ancestor_ids[level], sizeof(u64));



	cgid = cgroup_id(cgrp);

	memcpy(dest, &cgid, sizeof(u64));

	return true;

}

#endif

tools/perf/util/bpf_skel/bperf_cgroup.bpf.c

+1 −1
Original line number Diff line number Diff line
@@ -68,7 +68,7 @@ static inline int get_cgroup_v1_idx(__u32 *cgrps, int size) 
			break;



		// convert cgroup-id to a map index

		cgrp_id = BPF_CORE_READ(cgrp, ancestor_ids[i]);

		cgrp_id = BPF_CORE_READ(cgrp, ancestors[i], kn, id);

		elem = bpf_map_lookup_elem(&cgrp_idx, &cgrp_id);

		if (!elem)

			continue;