Commit 7d7efec3 authored by Tejun Heo's avatar Tejun Heo

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: default avatarTejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
parent 8ab456ac
......@@ -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 */
......@@ -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
......
......@@ -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;
......
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