--- /dev/null
+From stable+bounces-95988-greg=kroah.com@vger.kernel.org Mon Dec 2 12:11:04 2024
+From: Siddh Raman Pant <siddh.raman.pant@oracle.com>
+Date: Mon, 2 Dec 2024 16:40:23 +0530
+Subject: cgroup: Make operations on the cgroup root_list RCU safe
+To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+Cc: stable <stable@vger.kernel.org>, linux-kernel <linux-kernel@vger.kernel.org>
+Message-ID: <20241202111024.11212-2-siddh.raman.pant@oracle.com>
+
+From: Yafang Shao <laoar.shao@gmail.com>
+
+commit d23b5c577715892c87533b13923306acc6243f93 upstream.
+
+At present, when we perform operations on the cgroup root_list, we must
+hold the cgroup_mutex, which is a relatively heavyweight lock. In reality,
+we can make operations on this list RCU-safe, eliminating the need to hold
+the cgroup_mutex during traversal. Modifications to the list only occur in
+the cgroup root setup and destroy paths, which should be infrequent in a
+production environment. In contrast, traversal may occur frequently.
+Therefore, making it RCU-safe would be beneficial.
+
+Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
+Signed-off-by: Tejun Heo <tj@kernel.org>
+[fp: adapt to 5.10 mainly because of changes made by e210a89f5b07
+ ("cgroup.c: add helper __cset_cgroup_from_root to cleanup duplicated
+ codes")]
+Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
+[Shivani: Modified to apply on v5.4.y]
+Signed-off-by: Shivani Agarwal <shivani.agarwal@broadcom.com>
+Reviewed-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
+Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ include/linux/cgroup-defs.h | 1 +
+ kernel/cgroup/cgroup-internal.h | 3 ++-
+ kernel/cgroup/cgroup.c | 23 ++++++++++++++++-------
+ 3 files changed, 19 insertions(+), 8 deletions(-)
+
+--- a/include/linux/cgroup-defs.h
++++ b/include/linux/cgroup-defs.h
+@@ -517,6 +517,7 @@ struct cgroup_root {
+
+ /* A list running through the active hierarchies */
+ struct list_head root_list;
++ struct rcu_head rcu;
+
+ /* Hierarchy-specific flags */
+ unsigned int flags;
+--- a/kernel/cgroup/cgroup-internal.h
++++ b/kernel/cgroup/cgroup-internal.h
+@@ -172,7 +172,8 @@ extern struct list_head cgroup_roots;
+
+ /* iterate across the hierarchies */
+ #define for_each_root(root) \
+- list_for_each_entry((root), &cgroup_roots, root_list)
++ list_for_each_entry_rcu((root), &cgroup_roots, root_list, \
++ lockdep_is_held(&cgroup_mutex))
+
+ /**
+ * for_each_subsys - iterate all enabled cgroup subsystems
+--- a/kernel/cgroup/cgroup.c
++++ b/kernel/cgroup/cgroup.c
+@@ -1314,7 +1314,7 @@ void cgroup_free_root(struct cgroup_root
+ {
+ if (root) {
+ idr_destroy(&root->cgroup_idr);
+- kfree(root);
++ kfree_rcu(root, rcu);
+ }
+ }
+
+@@ -1348,7 +1348,7 @@ static void cgroup_destroy_root(struct c
+ spin_unlock_irq(&css_set_lock);
+
+ if (!list_empty(&root->root_list)) {
+- list_del(&root->root_list);
++ list_del_rcu(&root->root_list);
+ cgroup_root_count--;
+ }
+
+@@ -1401,7 +1401,6 @@ static struct cgroup *cset_cgroup_from_r
+ {
+ struct cgroup *res = NULL;
+
+- lockdep_assert_held(&cgroup_mutex);
+ lockdep_assert_held(&css_set_lock);
+
+ if (cset == &init_css_set) {
+@@ -1421,13 +1420,23 @@ static struct cgroup *cset_cgroup_from_r
+ }
+ }
+
+- BUG_ON(!res);
++ /*
++ * If cgroup_mutex is not held, the cgrp_cset_link will be freed
++ * before we remove the cgroup root from the root_list. Consequently,
++ * when accessing a cgroup root, the cset_link may have already been
++ * freed, resulting in a NULL res_cgroup. However, by holding the
++ * cgroup_mutex, we ensure that res_cgroup can't be NULL.
++ * If we don't hold cgroup_mutex in the caller, we must do the NULL
++ * check.
++ */
+ return res;
+ }
+
+ /*
+ * Return the cgroup for "task" from the given hierarchy. Must be
+- * called with cgroup_mutex and css_set_lock held.
++ * called with css_set_lock held to prevent task's groups from being modified.
++ * Must be called with either cgroup_mutex or rcu read lock to prevent the
++ * cgroup root from being destroyed.
+ */
+ struct cgroup *task_cgroup_from_root(struct task_struct *task,
+ struct cgroup_root *root)
+@@ -2012,7 +2021,7 @@ void init_cgroup_root(struct cgroup_fs_c
+ struct cgroup_root *root = ctx->root;
+ struct cgroup *cgrp = &root->cgrp;
+
+- INIT_LIST_HEAD(&root->root_list);
++ INIT_LIST_HEAD_RCU(&root->root_list);
+ atomic_set(&root->nr_cgrps, 1);
+ cgrp->root = root;
+ init_cgroup_housekeeping(cgrp);
+@@ -2094,7 +2103,7 @@ int cgroup_setup_root(struct cgroup_root
+ * care of subsystems' refcounts, which are explicitly dropped in
+ * the failure exit path.
+ */
+- list_add(&root->root_list, &cgroup_roots);
++ list_add_rcu(&root->root_list, &cgroup_roots);
+ cgroup_root_count++;
+
+ /*
--- /dev/null
+From stable+bounces-95989-greg=kroah.com@vger.kernel.org Mon Dec 2 12:11:20 2024
+From: Siddh Raman Pant <siddh.raman.pant@oracle.com>
+Date: Mon, 2 Dec 2024 16:40:24 +0530
+Subject: cgroup: Move rcu_head up near the top of cgroup_root
+To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+Cc: stable <stable@vger.kernel.org>, linux-kernel <linux-kernel@vger.kernel.org>
+Message-ID: <20241202111024.11212-3-siddh.raman.pant@oracle.com>
+
+From: Waiman Long <longman@redhat.com>
+
+commit a7fb0423c201ba12815877a0b5a68a6a1710b23a upstream.
+
+Commit d23b5c577715 ("cgroup: Make operations on the cgroup root_list RCU
+safe") adds a new rcu_head to the cgroup_root structure and kvfree_rcu()
+for freeing the cgroup_root.
+
+The current implementation of kvfree_rcu(), however, has the limitation
+that the offset of the rcu_head structure within the larger data
+structure must be less than 4096 or the compilation will fail. See the
+macro definition of __is_kvfree_rcu_offset() in include/linux/rcupdate.h
+for more information.
+
+By putting rcu_head below the large cgroup structure, any change to the
+cgroup structure that makes it larger run the risk of causing build
+failure under certain configurations. Commit 77070eeb8821 ("cgroup:
+Avoid false cacheline sharing of read mostly rstat_cpu") happens to be
+the last straw that breaks it. Fix this problem by moving the rcu_head
+structure up before the cgroup structure.
+
+Fixes: d23b5c577715 ("cgroup: Make operations on the cgroup root_list RCU safe")
+Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
+Closes: https://lore.kernel.org/lkml/20231207143806.114e0a74@canb.auug.org.au/
+Signed-off-by: Waiman Long <longman@redhat.com>
+Acked-by: Yafang Shao <laoar.shao@gmail.com>
+Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
+Reviewed-by: Michal Koutný <mkoutny@suse.com>
+Signed-off-by: Tejun Heo <tj@kernel.org>
+Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
+[Shivani: Modified to apply on v5.4.y]
+Signed-off-by: Shivani Agarwal <shivani.agarwal@broadcom.com>
+Reviewed-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
+Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ include/linux/cgroup-defs.h | 8 ++++----
+ 1 file changed, 4 insertions(+), 4 deletions(-)
+
+--- a/include/linux/cgroup-defs.h
++++ b/include/linux/cgroup-defs.h
+@@ -506,6 +506,10 @@ struct cgroup_root {
+ /* Unique id for this hierarchy. */
+ int hierarchy_id;
+
++ /* A list running through the active hierarchies */
++ struct list_head root_list;
++ struct rcu_head rcu;
++
+ /* The root cgroup. Root is destroyed on its release. */
+ struct cgroup cgrp;
+
+@@ -515,10 +519,6 @@ struct cgroup_root {
+ /* Number of cgroups in the hierarchy, used only for /proc/cgroups */
+ atomic_t nr_cgrps;
+
+- /* A list running through the active hierarchies */
+- struct list_head root_list;
+- struct rcu_head rcu;
+-
+ /* Hierarchy-specific flags */
+ unsigned int flags;
+
projects / thirdparty / kernel / stable-queue.git / commitdiff
