From ca8bdcaff0d77990fb69e0f946018c96a70851cc Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 26 Aug 2013 18:40:56 -0400 Subject: [PATCH] cgroup: make cgroup_css() take cgroup_subsys * instead and allow NULL subsys cgroup_css() is no longer used in hot paths. Make it take struct cgroup_subsys * and allow the users to specify NULL subsys to obtain the dummy_css. This removes open-coded NULL subsystem testing in a couple users and generally simplifies the code. After this patch, css_from_dir() also allows NULL @ss and returns the matching dummy_css. This behavior change doesn't affect its only user - perf. Signed-off-by: Tejun Heo Acked-by: Li Zefan Acked-by: Kirill A. Shutemov --- kernel/cgroup.c | 90 +++++++++++++++++++++++-------------------------- 1 file changed, 43 insertions(+), 47 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 921b1387c944..7516668d8325 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -226,19 +226,22 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], /** * cgroup_css - obtain a cgroup's css for the specified subsystem * @cgrp: the cgroup of interest - * @subsys_id: the subsystem of interest + * @ss: the subsystem of interest (%NULL returns the dummy_css) * - * 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. + * Return @cgrp's css (cgroup_subsys_state) associated with @ss. 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) + struct cgroup_subsys *ss) { - return rcu_dereference_check(cgrp->subsys[subsys_id], - lockdep_is_held(&cgroup_mutex)); + if (ss) + return rcu_dereference_check(cgrp->subsys[ss->subsys_id], + lockdep_is_held(&cgroup_mutex)); + else + return &cgrp->dummy_css; } /* convenient tests for these bits */ @@ -580,7 +583,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset, /* Subsystem is in this hierarchy. So we want * the subsystem state from the new * cgroup */ - template[i] = cgroup_css(cgrp, i); + template[i] = cgroup_css(cgrp, ss); } else { /* Subsystem is not in this hierarchy, so we * don't want to change the subsystem state */ @@ -1062,30 +1065,30 @@ static int rebind_subsystems(struct cgroupfs_root *root, if (bit & added_mask) { /* We're binding this subsystem to this hierarchy */ - BUG_ON(cgroup_css(cgrp, i)); - BUG_ON(!cgroup_css(cgroup_dummy_top, i)); - BUG_ON(cgroup_css(cgroup_dummy_top, i)->cgroup != cgroup_dummy_top); + BUG_ON(cgroup_css(cgrp, ss)); + BUG_ON(!cgroup_css(cgroup_dummy_top, ss)); + BUG_ON(cgroup_css(cgroup_dummy_top, ss)->cgroup != cgroup_dummy_top); rcu_assign_pointer(cgrp->subsys[i], - cgroup_css(cgroup_dummy_top, i)); - cgroup_css(cgrp, i)->cgroup = cgrp; + cgroup_css(cgroup_dummy_top, ss)); + cgroup_css(cgrp, ss)->cgroup = cgrp; list_move(&ss->sibling, &root->subsys_list); ss->root = root; if (ss->bind) - ss->bind(cgroup_css(cgrp, i)); + ss->bind(cgroup_css(cgrp, ss)); /* refcount was already taken, and we're keeping it */ root->subsys_mask |= bit; } else if (bit & removed_mask) { /* We're removing this subsystem */ - BUG_ON(cgroup_css(cgrp, i) != cgroup_css(cgroup_dummy_top, i)); - BUG_ON(cgroup_css(cgrp, i)->cgroup != cgrp); + BUG_ON(cgroup_css(cgrp, ss) != cgroup_css(cgroup_dummy_top, ss)); + BUG_ON(cgroup_css(cgrp, ss)->cgroup != cgrp); if (ss->bind) - ss->bind(cgroup_css(cgroup_dummy_top, i)); + ss->bind(cgroup_css(cgroup_dummy_top, ss)); - cgroup_css(cgroup_dummy_top, i)->cgroup = cgroup_dummy_top; + cgroup_css(cgroup_dummy_top, ss)->cgroup = cgroup_dummy_top; RCU_INIT_POINTER(cgrp->subsys[i], NULL); cgroup_subsys[i]->root = &cgroup_dummy_root; @@ -1930,7 +1933,7 @@ EXPORT_SYMBOL_GPL(cgroup_taskset_next); struct cgroup_subsys_state *cgroup_taskset_cur_css(struct cgroup_taskset *tset, int subsys_id) { - return cgroup_css(tset->cur_cgrp, subsys_id); + return cgroup_css(tset->cur_cgrp, cgroup_subsys[subsys_id]); } EXPORT_SYMBOL_GPL(cgroup_taskset_cur_css); @@ -2071,7 +2074,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk, * step 1: check that we can legitimately attach to the cgroup. */ for_each_root_subsys(root, ss) { - struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); + struct cgroup_subsys_state *css = cgroup_css(cgrp, ss); if (ss->can_attach) { retval = ss->can_attach(css, &tset); @@ -2113,7 +2116,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk, * step 4: do subsystem attach callbacks. */ for_each_root_subsys(root, ss) { - struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); + struct cgroup_subsys_state *css = cgroup_css(cgrp, ss); if (ss->attach) ss->attach(css, &tset); @@ -2135,7 +2138,7 @@ out_put_css_set_refs: out_cancel_attach: if (retval) { for_each_root_subsys(root, ss) { - struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); + struct cgroup_subsys_state *css = cgroup_css(cgrp, ss); if (ss == failed_ss) break; @@ -2481,13 +2484,9 @@ static int cgroup_file_open(struct inode *inode, struct file *file) * @css stays alive for all file operations. */ rcu_read_lock(); - if (cft->ss) { - css = cgroup_css(cgrp, cft->ss->subsys_id); - if (!css_tryget(css)) - css = NULL; - } else { - css = &cgrp->dummy_css; - } + css = cgroup_css(cgrp, cft->ss); + if (cft->ss && !css_tryget(css)) + css = NULL; rcu_read_unlock(); if (!css) @@ -2878,7 +2877,7 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add) /* add/rm files for all cgroups created before */ rcu_read_lock(); - css_for_each_descendant_pre(css, cgroup_css(root, ss->subsys_id)) { + css_for_each_descendant_pre(css, cgroup_css(root, ss)) { struct cgroup *cgrp = css->cgroup; if (cgroup_is_dead(cgrp)) @@ -3082,10 +3081,7 @@ css_next_child(struct cgroup_subsys_state *pos_css, if (&next->sibling == &cgrp->children) return NULL; - if (parent_css->ss) - return cgroup_css(next, parent_css->ss->subsys_id); - else - return &next->dummy_css; + return cgroup_css(next, parent_css->ss); } EXPORT_SYMBOL_GPL(css_next_child); @@ -4110,7 +4106,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css, rcu_read_lock(); ret = -EINVAL; - event->css = cgroup_css(cgrp, event->cft->ss->subsys_id); + event->css = cgroup_css(cgrp, event->cft->ss); if (event->css) ret = 0; @@ -4266,7 +4262,7 @@ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask) /* This cgroup is ready now */ for_each_root_subsys(cgrp->root, ss) { - struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); + struct cgroup_subsys_state *css = cgroup_css(cgrp, ss); struct css_id *id = rcu_dereference_protected(css->id, true); /* @@ -4349,11 +4345,11 @@ static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss, css->id = NULL; if (cgrp->parent) - css->parent = cgroup_css(cgrp->parent, ss->subsys_id); + css->parent = cgroup_css(cgrp->parent, ss); else css->flags |= CSS_ROOT; - BUG_ON(cgroup_css(cgrp, ss->subsys_id)); + BUG_ON(cgroup_css(cgrp, ss)); } /* invoke ->css_online() on a new CSS and mark it online if successful */ @@ -4466,7 +4462,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, for_each_root_subsys(root, ss) { struct cgroup_subsys_state *css; - css = ss->css_alloc(cgroup_css(parent, ss->subsys_id)); + css = ss->css_alloc(cgroup_css(parent, ss)); if (IS_ERR(css)) { err = PTR_ERR(css); goto err_free_all; @@ -4712,7 +4708,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) * percpu refs of all css's are confirmed to be killed. */ for_each_root_subsys(cgrp->root, ss) - kill_css(cgroup_css(cgrp, ss->subsys_id)); + kill_css(cgroup_css(cgrp, ss)); /* * Mark @cgrp dead. This prevents further task migration and child @@ -4839,7 +4835,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) /* Create the top cgroup state for this subsystem */ list_add(&ss->sibling, &cgroup_dummy_root.subsys_list); ss->root = &cgroup_dummy_root; - css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss->subsys_id)); + css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss)); /* We don't handle early failures gracefully */ BUG_ON(IS_ERR(css)); init_css(css, ss, cgroup_dummy_top); @@ -4918,7 +4914,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss) * struct, so this can happen first (i.e. before the dummy root * attachment). */ - css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss->subsys_id)); + css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss)); if (IS_ERR(css)) { /* failure case - need to deassign the cgroup_subsys[] slot. */ cgroup_subsys[ss->subsys_id] = NULL; @@ -5000,7 +4996,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) mutex_lock(&cgroup_mutex); - offline_css(cgroup_css(cgroup_dummy_top, ss->subsys_id)); + offline_css(cgroup_css(cgroup_dummy_top, ss)); if (ss->use_id) idr_destroy(&ss->idr); @@ -5034,7 +5030,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) * the cgrp->subsys pointer to find their state. note that this * also takes care of freeing the css_id. */ - ss->css_free(cgroup_css(cgroup_dummy_top, ss->subsys_id)); + ss->css_free(cgroup_css(cgroup_dummy_top, ss)); RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL); mutex_unlock(&cgroup_mutex); @@ -5721,7 +5717,7 @@ struct cgroup_subsys_state *css_from_dir(struct dentry *dentry, return ERR_PTR(-EBADF); cgrp = __d_cgrp(dentry); - return cgroup_css(cgrp, ss->subsys_id) ?: ERR_PTR(-ENOENT); + return cgroup_css(cgrp, ss) ?: ERR_PTR(-ENOENT); } /** -- 2.20.1