Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934548AbbEMUfg (ORCPT ); Wed, 13 May 2015 16:35:36 -0400 Received: from mail-qk0-f169.google.com ([209.85.220.169]:34555 "EHLO mail-qk0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932417AbbEMUfa (ORCPT ); Wed, 13 May 2015 16:35:30 -0400 From: Tejun Heo To: lizefan@huawei.com Cc: cgroups@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, linux-kernel@vger.kernel.org, Tejun Heo Subject: [PATCH 1/3] sched, cgroup: reorganize threadgroup locking Date: Wed, 13 May 2015 16:35:16 -0400 Message-Id: <1431549318-16756-2-git-send-email-tj@kernel.org> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1431549318-16756-1-git-send-email-tj@kernel.org> References: <1431549318-16756-1-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: 7202 Lines: 202 threadgroup_change_begin/end() are used to mark the beginning and end of threadgroup modifying operations to allow code paths which require a threadgroup to stay stable across blocking operations to synchronize against those sections using threadgroup_lock/unlock(). It's currently implemented as a general mechanism in sched.h using per-signal_struct rwsem; however, this never grew non-cgroup use cases and becomes noop if !CONFIG_CGROUPS. It turns out that cgroups is gonna be better served with a different sycnrhonization scheme and is a bit silly to keep cgroups specific details as a general mechanism. What's general here is identifying the places where threadgroups are modified. This patch restructures threadgroup locking so that threadgroup_change_begin/end() become a place where subsystems which need to sycnhronize against threadgroup changes can hook into. cgroup_threadgroup_change_begin/end() which operate on the per-signal_struct rwsem are created and threadgroup_lock/unlock() are moved to cgroup.c and made static. This is pure reorganization which doesn't cause any functional changes. Signed-off-by: Tejun Heo Cc: Ingo Molnar Cc: Peter Zijlstra --- include/linux/cgroup-defs.h | 10 +++++++++ include/linux/sched.h | 53 +++++++++++++++------------------------------ kernel/cgroup.c | 42 +++++++++++++++++++++++++++++++++++ 3 files changed, 69 insertions(+), 36 deletions(-) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 55f3120..1b8c938 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -14,6 +14,7 @@ #include #include #include +#include #include #ifdef CONFIG_CGROUPS @@ -460,5 +461,14 @@ struct cgroup_subsys { unsigned int depends_on; }; +void cgroup_threadgroup_change_begin(struct task_struct *tsk); +void cgroup_threadgroup_change_end(struct task_struct *tsk); + +#else /* CONFIG_CGROUPS */ + +static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk) {} +static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {} + #endif /* CONFIG_CGROUPS */ + #endif /* _LINUX_CGROUP_DEFS_H */ diff --git a/include/linux/sched.h b/include/linux/sched.h index 8222ae4..5ee2900 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -58,6 +58,7 @@ struct sched_param { #include #include #include +#include #include @@ -2648,53 +2649,33 @@ static inline void unlock_task_sighand(struct task_struct *tsk, spin_unlock_irqrestore(&tsk->sighand->siglock, *flags); } -#ifdef CONFIG_CGROUPS -static inline void threadgroup_change_begin(struct task_struct *tsk) -{ - down_read(&tsk->signal->group_rwsem); -} -static inline void threadgroup_change_end(struct task_struct *tsk) -{ - up_read(&tsk->signal->group_rwsem); -} - /** - * threadgroup_lock - lock threadgroup - * @tsk: member task of the threadgroup to lock - * - * Lock the threadgroup @tsk belongs to. No new task is allowed to enter - * and member tasks aren't allowed to exit (as indicated by PF_EXITING) or - * change ->group_leader/pid. This is useful for cases where the threadgroup - * needs to stay stable across blockable operations. + * threadgroup_change_begin - mark the beginning of changes to a threadgroup + * @tsk: task causing the changes * - * fork and exit paths explicitly call threadgroup_change_{begin|end}() for - * synchronization. While held, no new task will be added to threadgroup - * and no existing live task will have its PF_EXITING set. - * - * de_thread() does threadgroup_change_{begin|end}() when a non-leader - * sub-thread becomes a new leader. + * All operations which modify a threadgroup - a new thread joining the + * group, death of a member thread (the assertion of PF_EXITING) and + * exec(2) dethreading the process and replacing the leader - are wrapped + * by threadgroup_change_{begin|end}(). This is to provide a place which + * subsystems needing threadgroup stability can hook into for + * synchronization. */ -static inline void threadgroup_lock(struct task_struct *tsk) +static inline void threadgroup_change_begin(struct task_struct *tsk) { - down_write(&tsk->signal->group_rwsem); + might_sleep(); + cgroup_threadgroup_change_begin(tsk); } /** - * threadgroup_unlock - unlock threadgroup - * @tsk: member task of the threadgroup to unlock + * threadgroup_change_end - mark the end of changes to a threadgroup + * @tsk: task causing the changes * - * Reverse threadgroup_lock(). + * See threadgroup_change_begin(). */ -static inline void threadgroup_unlock(struct task_struct *tsk) +static inline void threadgroup_change_end(struct task_struct *tsk) { - up_write(&tsk->signal->group_rwsem); + cgroup_threadgroup_change_end(tsk); } -#else -static inline void threadgroup_change_begin(struct task_struct *tsk) {} -static inline void threadgroup_change_end(struct task_struct *tsk) {} -static inline void threadgroup_lock(struct task_struct *tsk) {} -static inline void threadgroup_unlock(struct task_struct *tsk) {} -#endif #ifndef __HAVE_THREAD_FUNCTIONS diff --git a/kernel/cgroup.c b/kernel/cgroup.c index cfa27f9..9309452 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -848,6 +848,48 @@ static struct css_set *find_css_set(struct css_set *old_cset, return cset; } +void cgroup_threadgroup_change_begin(struct task_struct *tsk) +{ + down_read(&tsk->signal->group_rwsem); +} + +void cgroup_threadgroup_change_end(struct task_struct *tsk) +{ + up_read(&tsk->signal->group_rwsem); +} + +/** + * threadgroup_lock - lock threadgroup + * @tsk: member task of the threadgroup to lock + * + * Lock the threadgroup @tsk belongs to. No new task is allowed to enter + * and member tasks aren't allowed to exit (as indicated by PF_EXITING) or + * change ->group_leader/pid. This is useful for cases where the threadgroup + * needs to stay stable across blockable operations. + * + * fork and exit explicitly call threadgroup_change_{begin|end}() for + * synchronization. While held, no new task will be added to threadgroup + * and no existing live task will have its PF_EXITING set. + * + * de_thread() does threadgroup_change_{begin|end}() when a non-leader + * sub-thread becomes a new leader. + */ +static void threadgroup_lock(struct task_struct *tsk) +{ + down_write(&tsk->signal->group_rwsem); +} + +/** + * threadgroup_unlock - unlock threadgroup + * @tsk: member task of the threadgroup to unlock + * + * Reverse threadgroup_lock(). + */ +static inline void threadgroup_unlock(struct task_struct *tsk) +{ + up_write(&tsk->signal->group_rwsem); +} + static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root) { struct cgroup *root_cgrp = kf_root->kn->priv; -- 2.1.0 -- 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/