sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem
Note: This commit was originally committed asd59cfc09c3but got reverted by0c986253b9due to the performance regression from the percpu_rwsem write down/up operations added to cgroup task migration path. percpu_rwsem changes which alleviate the performance issue are pending for v4.4-rc1 merge window. Re-apply. The cgroup side of threadgroup locking uses signal_struct->group_rwsem to synchronize against threadgroup changes. This per-process rwsem adds small overhead to thread creation, exit and exec paths, forces cgroup code paths to do lock-verify-unlock-retry dance in a couple places and makes it impossible to atomically perform operations across multiple processes. This patch replaces signal_struct->group_rwsem with a global percpu_rwsem cgroup_threadgroup_rwsem which is cheaper on the reader side and contained in cgroups proper. This patch converts one-to-one. This does make writer side heavier and lower the granularity; however, cgroup process migration is a fairly cold path, we do want to optimize thread operations over it and cgroup migration operations don't take enough time for the lower granularity to matter. Signed-off-by: Tejun Heo <tj@kernel.org> Link: http://lkml.kernel.org/g/55F8097A.7000206@de.ibm.com Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org>
This commit is contained in:
Tejun Heo
Родитель
0c986253b9
Коммит
1ed1328792
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@ -473,8 +473,31 @@ struct cgroup_subsys {
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unsigned int depends_on;
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};
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void cgroup_threadgroup_change_begin(struct task_struct *tsk);
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void cgroup_threadgroup_change_end(struct task_struct *tsk);
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extern struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
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/**
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* cgroup_threadgroup_change_begin - threadgroup exclusion for cgroups
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* @tsk: target task
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*
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* Called from threadgroup_change_begin() and allows cgroup operations to
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* synchronize against threadgroup changes using a percpu_rw_semaphore.
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*/
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static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk)
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{
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percpu_down_read(&cgroup_threadgroup_rwsem);
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}
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/**
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* cgroup_threadgroup_change_end - threadgroup exclusion for cgroups
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* @tsk: target task
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*
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* Called from threadgroup_change_end(). Counterpart of
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* cgroup_threadcgroup_change_begin().
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*/
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static inline void cgroup_threadgroup_change_end(struct task_struct *tsk)
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{
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percpu_up_read(&cgroup_threadgroup_rwsem);
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}
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#else /* CONFIG_CGROUPS */
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@ -25,13 +25,6 @@
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extern struct files_struct init_files;
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extern struct fs_struct init_fs;
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#ifdef CONFIG_CGROUPS
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#define INIT_GROUP_RWSEM(sig) \
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.group_rwsem = __RWSEM_INITIALIZER(sig.group_rwsem),
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#else
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#define INIT_GROUP_RWSEM(sig)
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#endif
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#ifdef CONFIG_CPUSETS
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#define INIT_CPUSET_SEQ(tsk) \
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.mems_allowed_seq = SEQCNT_ZERO(tsk.mems_allowed_seq),
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@ -64,7 +57,6 @@ extern struct fs_struct init_fs;
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INIT_PREV_CPUTIME(sig) \
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.cred_guard_mutex = \
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__MUTEX_INITIALIZER(sig.cred_guard_mutex), \
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INIT_GROUP_RWSEM(sig) \
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}
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extern struct nsproxy init_nsproxy;
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@ -762,18 +762,6 @@ struct signal_struct {
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unsigned audit_tty_log_passwd;
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struct tty_audit_buf *tty_audit_buf;
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#endif
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#ifdef CONFIG_CGROUPS
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/*
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* group_rwsem prevents new tasks from entering the threadgroup and
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* member tasks from exiting,a more specifically, setting of
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* PF_EXITING. fork and exit paths are protected with this rwsem
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* using threadgroup_change_begin/end(). Users which require
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* threadgroup to remain stable should use threadgroup_[un]lock()
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* which also takes care of exec path. Currently, cgroup is the
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* only user.
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*/
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struct rw_semaphore group_rwsem;
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#endif
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oom_flags_t oom_flags;
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short oom_score_adj; /* OOM kill score adjustment */
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@ -46,6 +46,7 @@
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <linux/rwsem.h>
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#include <linux/percpu-rwsem.h>
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#include <linux/string.h>
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#include <linux/sort.h>
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#include <linux/kmod.h>
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@ -103,6 +104,8 @@ static DEFINE_SPINLOCK(cgroup_idr_lock);
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*/
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static DEFINE_SPINLOCK(release_agent_path_lock);
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struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
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#define cgroup_assert_mutex_or_rcu_locked() \
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RCU_LOCKDEP_WARN(!rcu_read_lock_held() && \
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!lockdep_is_held(&cgroup_mutex), \
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@ -871,48 +874,6 @@ static struct css_set *find_css_set(struct css_set *old_cset,
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return cset;
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}
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void cgroup_threadgroup_change_begin(struct task_struct *tsk)
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{
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down_read(&tsk->signal->group_rwsem);
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}
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void cgroup_threadgroup_change_end(struct task_struct *tsk)
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{
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up_read(&tsk->signal->group_rwsem);
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}
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/**
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* threadgroup_lock - lock threadgroup
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* @tsk: member task of the threadgroup to lock
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*
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* Lock the threadgroup @tsk belongs to. No new task is allowed to enter
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* and member tasks aren't allowed to exit (as indicated by PF_EXITING) or
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* change ->group_leader/pid. This is useful for cases where the threadgroup
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* needs to stay stable across blockable operations.
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*
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* fork and exit explicitly call threadgroup_change_{begin|end}() for
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* synchronization. While held, no new task will be added to threadgroup
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* and no existing live task will have its PF_EXITING set.
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*
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* de_thread() does threadgroup_change_{begin|end}() when a non-leader
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* sub-thread becomes a new leader.
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*/
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static void threadgroup_lock(struct task_struct *tsk)
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{
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down_write(&tsk->signal->group_rwsem);
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}
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/**
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* threadgroup_unlock - unlock threadgroup
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* @tsk: member task of the threadgroup to unlock
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*
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* Reverse threadgroup_lock().
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*/
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static inline void threadgroup_unlock(struct task_struct *tsk)
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{
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up_write(&tsk->signal->group_rwsem);
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}
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static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
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{
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struct cgroup *root_cgrp = kf_root->kn->priv;
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@ -2113,9 +2074,9 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
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lockdep_assert_held(&css_set_rwsem);
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/*
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* We are synchronized through threadgroup_lock() against PF_EXITING
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* setting such that we can't race against cgroup_exit() changing the
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* css_set to init_css_set and dropping the old one.
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* We are synchronized through cgroup_threadgroup_rwsem against
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* PF_EXITING setting such that we can't race against cgroup_exit()
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* changing the css_set to init_css_set and dropping the old one.
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*/
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WARN_ON_ONCE(tsk->flags & PF_EXITING);
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old_cset = task_css_set(tsk);
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@ -2172,10 +2133,11 @@ static void cgroup_migrate_finish(struct list_head *preloaded_csets)
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* @src_cset and add it to @preloaded_csets, which should later be cleaned
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* up by cgroup_migrate_finish().
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*
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* This function may be called without holding threadgroup_lock even if the
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* target is a process. Threads may be created and destroyed but as long
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* as cgroup_mutex is not dropped, no new css_set can be put into play and
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* the preloaded css_sets are guaranteed to cover all migrations.
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* This function may be called without holding cgroup_threadgroup_rwsem
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* even if the target is a process. Threads may be created and destroyed
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* but as long as cgroup_mutex is not dropped, no new css_set can be put
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* into play and the preloaded css_sets are guaranteed to cover all
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* migrations.
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*/
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static void cgroup_migrate_add_src(struct css_set *src_cset,
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struct cgroup *dst_cgrp,
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@ -2278,7 +2240,7 @@ err:
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* @threadgroup: whether @leader points to the whole process or a single task
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*
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* Migrate a process or task denoted by @leader to @cgrp. If migrating a
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* process, the caller must be holding threadgroup_lock of @leader. The
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* process, the caller must be holding cgroup_threadgroup_rwsem. The
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* caller is also responsible for invoking cgroup_migrate_add_src() and
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* cgroup_migrate_prepare_dst() on the targets before invoking this
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* function and following up with cgroup_migrate_finish().
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@ -2406,7 +2368,7 @@ out_release_tset:
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* @leader: the task or the leader of the threadgroup to be attached
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* @threadgroup: attach the whole threadgroup?
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*
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* Call holding cgroup_mutex and threadgroup_lock of @leader.
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* Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
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*/
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static int cgroup_attach_task(struct cgroup *dst_cgrp,
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struct task_struct *leader, bool threadgroup)
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@ -2528,7 +2490,7 @@ retry_find_task:
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get_task_struct(tsk);
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rcu_read_unlock();
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threadgroup_lock(tsk);
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percpu_down_write(&cgroup_threadgroup_rwsem);
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if (threadgroup) {
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if (!thread_group_leader(tsk)) {
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/*
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@ -2538,7 +2500,7 @@ retry_find_task:
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* try again; this is
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* "double-double-toil-and-trouble-check locking".
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*/
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threadgroup_unlock(tsk);
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percpu_up_write(&cgroup_threadgroup_rwsem);
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put_task_struct(tsk);
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goto retry_find_task;
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}
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@ -2548,7 +2510,7 @@ retry_find_task:
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if (!ret)
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ret = cgroup_attach_task(cgrp, tsk, threadgroup);
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threadgroup_unlock(tsk);
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percpu_up_write(&cgroup_threadgroup_rwsem);
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put_task_struct(tsk);
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out_unlock_cgroup:
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@ -2751,17 +2713,17 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
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goto out_finish;
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last_task = task;
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threadgroup_lock(task);
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percpu_down_write(&cgroup_threadgroup_rwsem);
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/* raced against de_thread() from another thread? */
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if (!thread_group_leader(task)) {
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threadgroup_unlock(task);
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percpu_up_write(&cgroup_threadgroup_rwsem);
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put_task_struct(task);
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continue;
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}
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ret = cgroup_migrate(src_cset->dfl_cgrp, task, true);
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threadgroup_unlock(task);
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percpu_up_write(&cgroup_threadgroup_rwsem);
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put_task_struct(task);
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if (WARN(ret, "cgroup: failed to update controllers for the default hierarchy (%d), further operations may crash or hang\n", ret))
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@ -5083,6 +5045,7 @@ int __init cgroup_init(void)
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unsigned long key;
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int ssid, err;
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BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
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BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
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BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
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@ -1149,10 +1149,6 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
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tty_audit_fork(sig);
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sched_autogroup_fork(sig);
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#ifdef CONFIG_CGROUPS
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init_rwsem(&sig->group_rwsem);
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#endif
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sig->oom_score_adj = current->signal->oom_score_adj;
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sig->oom_score_adj_min = current->signal->oom_score_adj_min;
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