Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751053Ab2JaEW4 (ORCPT ); Wed, 31 Oct 2012 00:22:56 -0400 Received: from mail-da0-f46.google.com ([209.85.210.46]:32779 "EHLO mail-da0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750831Ab2JaEWx (ORCPT ); Wed, 31 Oct 2012 00:22:53 -0400 From: Tejun Heo To: lizefan@huawei.com, hannes@cmpxchg.org, mhocko@suse.cz, bsingharora@gmail.com, kamezawa.hiroyu@jp.fujitsu.com Cc: containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Tejun Heo Subject: [PATCH 1/8] cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs Date: Tue, 30 Oct 2012 21:22:38 -0700 Message-Id: <1351657365-25055-2-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.7.11.7 In-Reply-To: <1351657365-25055-1-git-send-email-tj@kernel.org> References: <1351657365-25055-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9665 Lines: 292 2ef37d3fe4 ("memcg: Simplify mem_cgroup_force_empty_list error handling") removed the last user of __DEPRECATED_clear_css_refs. This patch removes __DEPRECATED_clear_css_refs and mechanisms to support it. * Conditionals dependent on __DEPRECATED_clear_css_refs removed. * ->pre_destroy() now can only fail if a new task is attached or child cgroup is created while ->pre_destroy()s are being called. As the condition is checked again after re-acquiring cgroup_mutex afterwards, we don't need to take any immediate action on ->pre_destroy() failures. This reduces cgroup_call_pre_destroy() to a simple loop surrounding ->pre_destory(). Remove cgroup_call_pre_destroy() and open-code the loop into cgroup_rmdir(). * cgroup_clear_css_refs() can no longer fail. All that needs to be done are deactivating refcnts, setting CSS_REMOVED and putting the base reference on each css. Remove cgroup_clear_css_refs() and the failure path, and open-code the loops into cgroup_rmdir(). Note that cgroup_rmdir() will see more cleanup soon. Signed-off-by: Tejun Heo --- include/linux/cgroup.h | 12 ---- kernel/cgroup.c | 159 ++++++++++++------------------------------------- 2 files changed, 38 insertions(+), 133 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index c90eaa8..02e09c0 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -86,7 +86,6 @@ struct cgroup_subsys_state { enum { CSS_ROOT, /* This CSS is the root of the subsystem */ CSS_REMOVED, /* This CSS is dead */ - CSS_CLEAR_CSS_REFS, /* @ss->__DEPRECATED_clear_css_refs */ }; /* Caller must verify that the css is not for root cgroup */ @@ -485,17 +484,6 @@ struct cgroup_subsys { */ bool use_id; - /* - * If %true, cgroup removal will try to clear css refs by retrying - * ss->pre_destroy() until there's no css ref left. This behavior - * is strictly for backward compatibility and will be removed as - * soon as the current user (memcg) is updated. - * - * If %false, ss->pre_destroy() can't fail and cgroup removal won't - * wait for css refs to drop to zero before proceeding. - */ - bool __DEPRECATED_clear_css_refs; - #define MAX_CGROUP_TYPE_NAMELEN 32 const char *name; diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 7981850..033bf4b 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -851,30 +851,6 @@ static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb) return inode; } -/* - * Call subsys's pre_destroy handler. - * This is called before css refcnt check. - */ -static int cgroup_call_pre_destroy(struct cgroup *cgrp) -{ - struct cgroup_subsys *ss; - int ret = 0; - - for_each_subsys(cgrp->root, ss) { - if (!ss->pre_destroy) - continue; - - ret = ss->pre_destroy(cgrp); - if (ret) { - /* ->pre_destroy() failure is being deprecated */ - WARN_ON_ONCE(!ss->__DEPRECATED_clear_css_refs); - break; - } - } - - return ret; -} - static void cgroup_diput(struct dentry *dentry, struct inode *inode) { /* is dentry a directory ? if so, kfree() associated cgroup */ @@ -3901,14 +3877,12 @@ static void init_cgroup_css(struct cgroup_subsys_state *css, cgrp->subsys[ss->subsys_id] = css; /* - * If !clear_css_refs, css holds an extra ref to @cgrp->dentry - * which is put on the last css_put(). dput() requires process - * context, which css_put() may be called without. @css->dput_work - * will be used to invoke dput() asynchronously from css_put(). + * css holds an extra ref to @cgrp->dentry which is put on the last + * css_put(). dput() requires process context, which css_put() may + * be called without. @css->dput_work will be used to invoke + * dput() asynchronously from css_put(). */ INIT_WORK(&css->dput_work, css_dput_fn); - if (ss->__DEPRECATED_clear_css_refs) - set_bit(CSS_CLEAR_CSS_REFS, &css->flags); } /* @@ -3978,10 +3952,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, if (err < 0) goto err_remove; - /* If !clear_css_refs, each css holds a ref to the cgroup's dentry */ + /* each css holds a ref to the cgroup's dentry */ for_each_subsys(root, ss) - if (!ss->__DEPRECATED_clear_css_refs) - dget(dentry); + dget(dentry); /* The cgroup directory was pre-locked for us */ BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex)); @@ -4066,71 +4039,6 @@ static int cgroup_has_css_refs(struct cgroup *cgrp) return 0; } -/* - * Atomically mark all (or else none) of the cgroup's CSS objects as - * CSS_REMOVED. Return true on success, or false if the cgroup has - * busy subsystems. Call with cgroup_mutex held - * - * Depending on whether a subsys has __DEPRECATED_clear_css_refs set or - * not, cgroup removal behaves differently. - * - * If clear is set, css refcnt for the subsystem should be zero before - * cgroup removal can be committed. This is implemented by - * CGRP_WAIT_ON_RMDIR and retry logic around ->pre_destroy(), which may be - * called multiple times until all css refcnts reach zero and is allowed to - * veto removal on any invocation. This behavior is deprecated and will be - * removed as soon as the existing user (memcg) is updated. - * - * If clear is not set, each css holds an extra reference to the cgroup's - * dentry and cgroup removal proceeds regardless of css refs. - * ->pre_destroy() will be called at least once and is not allowed to fail. - * On the last put of each css, whenever that may be, the extra dentry ref - * is put so that dentry destruction happens only after all css's are - * released. - */ -static int cgroup_clear_css_refs(struct cgroup *cgrp) -{ - struct cgroup_subsys *ss; - unsigned long flags; - bool failed = false; - - local_irq_save(flags); - - /* - * Block new css_tryget() by deactivating refcnt. If all refcnts - * for subsystems w/ clear_css_refs set were 1 at the moment of - * deactivation, we succeeded. - */ - for_each_subsys(cgrp->root, ss) { - struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; - - WARN_ON(atomic_read(&css->refcnt) < 0); - atomic_add(CSS_DEACT_BIAS, &css->refcnt); - - if (ss->__DEPRECATED_clear_css_refs) - failed |= css_refcnt(css) != 1; - } - - /* - * If succeeded, set REMOVED and put all the base refs; otherwise, - * restore refcnts to positive values. Either way, all in-progress - * css_tryget() will be released. - */ - for_each_subsys(cgrp->root, ss) { - struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; - - if (!failed) { - set_bit(CSS_REMOVED, &css->flags); - css_put(css); - } else { - atomic_sub(CSS_DEACT_BIAS, &css->refcnt); - } - } - - local_irq_restore(flags); - return !failed; -} - static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry) { struct cgroup *cgrp = dentry->d_fsdata; @@ -4138,10 +4046,9 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry) struct cgroup *parent; DEFINE_WAIT(wait); struct cgroup_event *event, *tmp; - int ret; + struct cgroup_subsys *ss; /* the vfs holds both inode->i_mutex already */ -again: mutex_lock(&cgroup_mutex); if (atomic_read(&cgrp->count) != 0) { mutex_unlock(&cgroup_mutex); @@ -4168,11 +4075,9 @@ again: * Call pre_destroy handlers of subsys. Notify subsystems * that rmdir() request comes. */ - ret = cgroup_call_pre_destroy(cgrp); - if (ret) { - clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); - return ret; - } + for_each_subsys(cgrp->root, ss) + if (ss->pre_destroy) + WARN_ON_ONCE(ss->pre_destroy(cgrp)); mutex_lock(&cgroup_mutex); parent = cgrp->parent; @@ -4182,21 +4087,34 @@ again: return -EBUSY; } prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE); - if (!cgroup_clear_css_refs(cgrp)) { - mutex_unlock(&cgroup_mutex); - /* - * Because someone may call cgroup_wakeup_rmdir_waiter() before - * prepare_to_wait(), we need to check this flag. - */ - if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)) - schedule(); - finish_wait(&cgroup_rmdir_waitq, &wait); - clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); - if (signal_pending(current)) - return -EINTR; - goto again; + + local_irq_disable(); + + /* block new css_tryget() by deactivating refcnt */ + for_each_subsys(cgrp->root, ss) { + struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; + + WARN_ON(atomic_read(&css->refcnt) < 0); + atomic_add(CSS_DEACT_BIAS, &css->refcnt); } - /* NO css_tryget() can success after here. */ + + /* + * Set REMOVED. All in-progress css_tryget() will be released. + * Put all the base refs. Each css holds an extra reference to the + * cgroup's dentry and cgroup removal proceeds regardless of css + * refs. On the last put of each css, whenever that may be, the + * extra dentry ref is put so that dentry destruction happens only + * after all css's are released. + */ + for_each_subsys(cgrp->root, ss) { + struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; + + set_bit(CSS_REMOVED, &css->flags); + css_put(css); + } + + local_irq_enable(); + finish_wait(&cgroup_rmdir_waitq, &wait); clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); @@ -4949,8 +4867,7 @@ void __css_put(struct cgroup_subsys_state *css) cgroup_wakeup_rmdir_waiter(cgrp); break; case 0: - if (!test_bit(CSS_CLEAR_CSS_REFS, &css->flags)) - schedule_work(&css->dput_work); + schedule_work(&css->dput_work); break; } rcu_read_unlock(); -- 1.7.11.7 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/