From 73e80ed8007fc48a6deeb295ba37159fad274bd2 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 13 Aug 2013 11:01:55 -0400 Subject: [PATCH] cgroup: add __rcu modifier to cgroup->subsys[] For the planned unified hierarchy, each css (cgroup_subsys_state) will be RCU protected so that it can be created and destroyed individually while allowing RCU accesses. Previous changes ensured that all cgroup->subsys[] accesses use the cgroup_css() accessor. This patch adds __rcu modifier to cgroup->subsys[], add matching RCU dereference in cgroup_css() and convert all assignments to either rcu_assign_pointer() or RCU_INIT_POINTER(). This change prepares for the actual RCUfication of css's and doesn't introduce any visible behavior change. The conversion is verified with sparse and all accesses are properly RCU annotated. Signed-off-by: Tejun Heo Acked-by: Li Zefan --- include/linux/cgroup.h | 2 +- kernel/cgroup.c | 19 ++++++++++++++----- 2 files changed, 15 insertions(+), 6 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 8a5dc91fbaad..eb200b5794e7 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -204,7 +204,7 @@ struct cgroup { struct cgroup_name __rcu *name; /* Private pointers for each registered subsystem */ - struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT]; + struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT]; struct cgroupfs_root *root; diff --git a/kernel/cgroup.c b/kernel/cgroup.c index d63beffd41e1..c27101622567 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -229,11 +229,16 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], * @subsys_id: the subsystem of interest * * Return @cgrp's css (cgroup_subsys_state) associated with @subsys_id. + * This function must be called either under cgroup_mutex or + * rcu_read_lock() and the caller is responsible for pinning the returned + * css if it wants to keep accessing it outside the said locks. This + * function may return %NULL if @cgrp doesn't have @subsys_id enabled. */ static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp, int subsys_id) { - return cgrp->subsys[subsys_id]; + return rcu_dereference_check(cgrp->subsys[subsys_id], + lockdep_is_held(&cgroup_mutex)); } /* convenient tests for these bits */ @@ -1072,8 +1077,10 @@ static int rebind_subsystems(struct cgroupfs_root *root, BUG_ON(!cgroup_css(cgroup_dummy_top, i)); BUG_ON(cgroup_css(cgroup_dummy_top, i)->cgroup != cgroup_dummy_top); - cgrp->subsys[i] = cgroup_dummy_top->subsys[i]; + rcu_assign_pointer(cgrp->subsys[i], + cgroup_css(cgroup_dummy_top, i)); cgroup_css(cgrp, i)->cgroup = cgrp; + list_move(&ss->sibling, &root->subsys_list); ss->root = root; if (ss->bind) @@ -1088,8 +1095,10 @@ static int rebind_subsystems(struct cgroupfs_root *root, if (ss->bind) ss->bind(cgroup_css(cgroup_dummy_top, i)); + cgroup_css(cgroup_dummy_top, i)->cgroup = cgroup_dummy_top; - cgrp->subsys[i] = NULL; + RCU_INIT_POINTER(cgrp->subsys[i], NULL); + cgroup_subsys[i]->root = &cgroup_dummy_root; list_move(&ss->sibling, &cgroup_dummy_root.subsys_list); @@ -4314,7 +4323,7 @@ static void init_cgroup_css(struct cgroup_subsys_state *css, css->flags |= CSS_ROOT; BUG_ON(cgroup_css(cgrp, ss->subsys_id)); - cgrp->subsys[ss->subsys_id] = css; + rcu_assign_pointer(cgrp->subsys[ss->subsys_id], css); } /* invoke ->css_online() on a new CSS and mark it online if successful */ @@ -4962,7 +4971,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) * also takes care of freeing the css_id. */ ss->css_free(cgroup_css(cgroup_dummy_top, ss->subsys_id)); - cgroup_dummy_top->subsys[ss->subsys_id] = NULL; + RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL); mutex_unlock(&cgroup_mutex); } -- 2.20.1