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author | Tejun Heo <tj@kernel.org> | 2015-05-13 16:35:16 -0400 |
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committer | Tejun Heo <tj@kernel.org> | 2015-05-26 20:35:00 -0400 |
commit | 7d7efec368d537226142cbe559f45797f18672f9 (patch) | |
tree | 8b391dada2b97b66f9fbd4315b397516f13199de | |
parent | 8ab456ac3697dbd1d3eae5d5817dba941faf89ee (diff) | |
download | linux-7d7efec368d537226142cbe559f45797f18672f9.tar.gz linux-7d7efec368d537226142cbe559f45797f18672f9.tar.bz2 linux-7d7efec368d537226142cbe559f45797f18672f9.zip |
sched, cgroup: reorganize threadgroup locking
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 <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
-rw-r--r-- | include/linux/cgroup-defs.h | 10 | ||||
-rw-r--r-- | include/linux/sched.h | 53 | ||||
-rw-r--r-- | 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 55f3120fb952..1b8c93806dbd 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -14,6 +14,7 @@ #include <linux/mutex.h> #include <linux/rcupdate.h> #include <linux/percpu-refcount.h> +#include <linux/percpu-rwsem.h> #include <linux/workqueue.h> #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 8222ae40ecb0..5ee290003470 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -58,6 +58,7 @@ struct sched_param { #include <linux/uidgid.h> #include <linux/gfp.h> #include <linux/magic.h> +#include <linux/cgroup-defs.h> #include <asm/processor.h> @@ -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 b91177f93416..980b1f52f39f 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; |