diff options
Diffstat (limited to 'include/linux/sched.h')
| -rw-r--r-- | include/linux/sched.h | 73 |
1 files changed, 54 insertions, 19 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index ad93e1ec8c6..f044f66018f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -637,13 +637,15 @@ struct signal_struct { #endif #ifdef CONFIG_CGROUPS /* - * The threadgroup_fork_lock prevents threads from forking with - * CLONE_THREAD while held for writing. Use this for fork-sensitive - * threadgroup-wide operations. It's taken for reading in fork.c in - * copy_process(). - * Currently only needed write-side by cgroups. + * group_rwsem prevents new tasks from entering the threadgroup and + * member tasks from exiting,a more specifically, setting of + * PF_EXITING. fork and exit paths are protected with this rwsem + * using threadgroup_change_begin/end(). Users which require + * threadgroup to remain stable should use threadgroup_[un]lock() + * which also takes care of exec path. Currently, cgroup is the + * only user. */ - struct rw_semaphore threadgroup_fork_lock; + struct rw_semaphore group_rwsem; #endif int oom_adj; /* OOM kill score adjustment (bit shift) */ @@ -2394,29 +2396,62 @@ static inline void unlock_task_sighand(struct task_struct *tsk, spin_unlock_irqrestore(&tsk->sighand->siglock, *flags); } -/* See the declaration of threadgroup_fork_lock in signal_struct. */ #ifdef CONFIG_CGROUPS -static inline void threadgroup_fork_read_lock(struct task_struct *tsk) +static inline void threadgroup_change_begin(struct task_struct *tsk) { - down_read(&tsk->signal->threadgroup_fork_lock); + down_read(&tsk->signal->group_rwsem); } -static inline void threadgroup_fork_read_unlock(struct task_struct *tsk) +static inline void threadgroup_change_end(struct task_struct *tsk) { - up_read(&tsk->signal->threadgroup_fork_lock); + up_read(&tsk->signal->group_rwsem); } -static inline void threadgroup_fork_write_lock(struct task_struct *tsk) + +/** + * 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 + * perform exec. This is useful for cases where the threadgroup needs to + * stay stable across blockable operations. + * + * 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. + * + * During exec, a task goes and puts its thread group through unusual + * changes. After de-threading, exclusive access is assumed to resources + * which are usually shared by tasks in the same group - e.g. sighand may + * be replaced with a new one. Also, the exec'ing task takes over group + * leader role including its pid. Exclude these changes while locked by + * grabbing cred_guard_mutex which is used to synchronize exec path. + */ +static inline void threadgroup_lock(struct task_struct *tsk) { - down_write(&tsk->signal->threadgroup_fork_lock); + /* + * exec uses exit for de-threading nesting group_rwsem inside + * cred_guard_mutex. Grab cred_guard_mutex first. + */ + mutex_lock(&tsk->signal->cred_guard_mutex); + down_write(&tsk->signal->group_rwsem); } -static inline void threadgroup_fork_write_unlock(struct task_struct *tsk) + +/** + * 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->threadgroup_fork_lock); + up_write(&tsk->signal->group_rwsem); + mutex_unlock(&tsk->signal->cred_guard_mutex); } #else -static inline void threadgroup_fork_read_lock(struct task_struct *tsk) {} -static inline void threadgroup_fork_read_unlock(struct task_struct *tsk) {} -static inline void threadgroup_fork_write_lock(struct task_struct *tsk) {} -static inline void threadgroup_fork_write_unlock(struct task_struct *tsk) {} +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 |