From 257058ae2b971646b96ab3a15605ac69186e562a Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 12 Dec 2011 18:12:21 -0800 Subject: threadgroup: rename signal->threadgroup_fork_lock to ->group_rwsem Make the following renames to prepare for extension of threadgroup locking. * s/signal->threadgroup_fork_lock/signal->group_rwsem/ * s/threadgroup_fork_read_lock()/threadgroup_change_begin()/ * s/threadgroup_fork_read_unlock()/threadgroup_change_end()/ * s/threadgroup_fork_write_lock()/threadgroup_lock()/ * s/threadgroup_fork_write_unlock()/threadgroup_unlock()/ This patch doesn't cause any behavior change. -v2: Rename threadgroup_change_done() to threadgroup_change_end() per KAMEZAWA's suggestion. Signed-off-by: Tejun Heo Reviewed-by: KAMEZAWA Hiroyuki Acked-by: Li Zefan Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage --- include/linux/sched.h | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) (limited to 'include/linux/sched.h') diff --git a/include/linux/sched.h b/include/linux/sched.h index d81cce933869..8cd523202a3b 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -635,13 +635,13 @@ struct signal_struct { #endif #ifdef CONFIG_CGROUPS /* - * The threadgroup_fork_lock prevents threads from forking with + * The group_rwsem 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. */ - struct rw_semaphore threadgroup_fork_lock; + struct rw_semaphore group_rwsem; #endif int oom_adj; /* OOM kill score adjustment (bit shift) */ @@ -2371,29 +2371,29 @@ 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. */ +/* See the declaration of group_rwsem 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) +static inline void threadgroup_lock(struct task_struct *tsk) { - down_write(&tsk->signal->threadgroup_fork_lock); + down_write(&tsk->signal->group_rwsem); } -static inline void threadgroup_fork_write_unlock(struct task_struct *tsk) +static inline void threadgroup_unlock(struct task_struct *tsk) { - up_write(&tsk->signal->threadgroup_fork_lock); + up_write(&tsk->signal->group_rwsem); } #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 -- cgit v1.2.3 From 77e4ef99d1c596a31747668e5fd837f77b6349b6 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 12 Dec 2011 18:12:21 -0800 Subject: threadgroup: extend threadgroup_lock() to cover exit and exec threadgroup_lock() protected only protected against new addition to the threadgroup, which was inherently somewhat incomplete and problematic for its only user cgroup. On-going migration could race against exec and exit leading to interesting problems - the symmetry between various attach methods, task exiting during method execution, ->exit() racing against attach methods, migrating task switching basic properties during exec and so on. This patch extends threadgroup_lock() such that it protects against all three threadgroup altering operations - fork, exit and exec. For exit, threadgroup_change_begin/end() calls are added to exit_signals around assertion of PF_EXITING. For exec, threadgroup_[un]lock() are updated to also grab and release cred_guard_mutex. With this change, threadgroup_lock() guarantees that the target threadgroup will remain stable - no new task will be added, no new PF_EXITING will be set and exec won't happen. The next patch will update cgroup so that it can take full advantage of this change. -v2: beefed up comment as suggested by Frederic. -v3: narrowed scope of protection in exit path as suggested by Frederic. Signed-off-by: Tejun Heo Reviewed-by: KAMEZAWA Hiroyuki Acked-by: Li Zefan Acked-by: Frederic Weisbecker Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage Cc: Linus Torvalds --- include/linux/sched.h | 47 +++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 41 insertions(+), 6 deletions(-) (limited to 'include/linux/sched.h') diff --git a/include/linux/sched.h b/include/linux/sched.h index 8cd523202a3b..c0c5876c52c0 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -635,11 +635,13 @@ struct signal_struct { #endif #ifdef CONFIG_CGROUPS /* - * The group_rwsem 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 group_rwsem; #endif @@ -2371,7 +2373,6 @@ static inline void unlock_task_sighand(struct task_struct *tsk, spin_unlock_irqrestore(&tsk->sighand->siglock, *flags); } -/* See the declaration of group_rwsem in signal_struct. */ #ifdef CONFIG_CGROUPS static inline void threadgroup_change_begin(struct task_struct *tsk) { @@ -2381,13 +2382,47 @@ 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 + * 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) { + /* + * 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); } + +/** + * 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); + mutex_unlock(&tsk->signal->cred_guard_mutex); } #else static inline void threadgroup_change_begin(struct task_struct *tsk) {} -- cgit v1.2.3