Adds functionality to read/write lock CLONE_THREAD fork()ing per-threadgroup
From: Ben Blum <bb...@andrew.cmu.edu>
This patch adds an rwsem that lives in a threadgroup's sighand_struct (next to
the sighand's atomic count, to piggyback on its cacheline), and two functions
in kernel/cgroup.c (for now) for easily+safely obtaining and releasing it. If
another part of the kernel later wants to use such a locking mechanism, the
CONFIG_CGROUPS ifdefs should be changed to a higher-up flag that CGROUPS and
the other system would both depend on, and the lock/unlock functions could be
moved to sched.c or so.
This is a pre-patch for cgroups-procs-write.patch.
Signed-off-by: Ben Blum <bb...@andrew.cmu.edu>
---
include/linux/cgroup.h | 14 +++++--
include/linux/init_task.h | 9 ++++
include/linux/sched.h | 15 +++++++
kernel/cgroup.c | 93 ++++++++++++++++++++++++++++++++++++++++++++-
kernel/fork.c | 9 +++-
5 files changed, 131 insertions(+), 9 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 9be4c22..2eb54bb 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -30,10 +30,12 @@ extern int cgroup_init(void);
extern void cgroup_lock(void);
extern bool cgroup_lock_live_group(struct cgroup *cgrp);
extern void cgroup_unlock(void);
-extern void cgroup_fork(struct task_struct *p);
+extern void cgroup_fork(struct task_struct *p, unsigned long clone_flags);
extern void cgroup_fork_callbacks(struct task_struct *p);
-extern void cgroup_post_fork(struct task_struct *p);
+extern void cgroup_post_fork(struct task_struct *p, unsigned long clone_flags);
extern void cgroup_exit(struct task_struct *p, int run_callbacks);
+extern void cgroup_fork_failed(struct task_struct *p, int run_callbacks,
+ unsigned long clone_flags);
extern int cgroupstats_build(struct cgroupstats *stats,
struct dentry *dentry);
extern int cgroup_load_subsys(struct cgroup_subsys *ss);
@@ -580,10 +582,14 @@ unsigned short css_depth(struct cgroup_subsys_state *css);
static inline int cgroup_init_early(void) { return 0; }
static inline int cgroup_init(void) { return 0; }
-static inline void cgroup_fork(struct task_struct *p) {}
+static inline void cgroup_fork(struct task_struct *p,
+ unsigned long clone_flags) {}
static inline void cgroup_fork_callbacks(struct task_struct *p) {}
-static inline void cgroup_post_fork(struct task_struct *p) {}
+static inline void cgroup_post_fork(struct task_struct *p,
+ unsigned long clone_flags) {}
static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
+static inline void cgroup_fork_failed(struct task_struct *p, int callbacks,
+ unsigned long clone_flags) {}
static inline void cgroup_lock(void) {}
static inline void cgroup_unlock(void) {}
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 8ed0abf..aaa4b9c 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -41,7 +41,16 @@ extern struct nsproxy init_nsproxy;
INIT_IPC_NS(ipc_ns) \
}
+#ifdef CONFIG_CGROUPS
+# define INIT_THREADGROUP_FORK_LOCK(sighand) \
+ .threadgroup_fork_lock = \
+ __RWSEM_INITIALIZER(sighand.threadgroup_fork_lock),
+#else
+# define INIT_THREADGROUP_FORK_LOCK(sighand)
+#endif
+
#define INIT_SIGHAND(sighand) {
\
+ INIT_THREADGROUP_FORK_LOCK(sighand) \
.count = ATOMIC_INIT(1), \
.action = { { { .sa_handler = NULL, } }, }, \
.siglock = __SPIN_LOCK_UNLOCKED(sighand.siglock), \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 23b26c7..10a22a5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -475,6 +475,21 @@ extern int get_dumpable(struct mm_struct *mm);
#define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
struct sighand_struct {
+#ifdef CONFIG_CGROUPS
+ /*
+ * The threadgroup_fork_lock is used to prevent any threads in a
+ * threadgroup from forking with CLONE_THREAD while held for writing,
+ * used for threadgroup-wide operations that are fork-sensitive. It
+ * lives here next to sighand.count as a cacheline optimization.
+ *
+ * TODO: if anybody besides cgroups uses this lock, change the
+ * CONFIG_CGROUPS to a higher-up CONFIG_* that the other user and
+ * cgroups would both depend upon. Also, they'll want to move where
+ * the readlock happens - it currently lives in kernel/cgroup.c in
+ * cgroup_{fork,post_fork,fork_failed}().
+ */
+ struct rw_semaphore threadgroup_fork_lock;
+#endif
atomic_t count;
struct k_sigaction action[_NSIG];
spinlock_t siglock;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index cc2e1f6..99782a0 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1623,6 +1623,71 @@ int cgroup_path(const struct cgroup *cgrp, char *buf,
int buflen)
}
/**
+ * threadgroup_fork_lock - block all CLONE_THREAD forks in the threadgroup
+ * @tsk: the task whose threadgroup should be locked
+ *
+ * Takes the threadgroup_lock_mutex in the threadgroup's sighand_struct, by
+ * means of searching the threadgroup list for a live thread in the group.
+ * Returns the sighand_struct that should be given to threadgroup_fork_unlock,
+ * or -ESRCH if all threads in the group are exiting and have cleared their
+ * sighand pointers, or -EAGAIN if tsk is not the threadgroup leader.
+ */
+struct sighand_struct *threadgroup_fork_lock(struct task_struct *tsk)
+{
+ struct sighand_struct *sighand;
+ struct task_struct *p;
+
+ /* tasklist lock protects sighand_struct's disappearance in exit(). */
+ read_lock(&tasklist_lock);
+
+ /* make sure the threadgroup's state is sane before we proceed */
+ if (unlikely(!thread_group_leader(tsk))) {
+ /* a race with de_thread() stripped us of our leadership */
+ read_unlock(&tasklist_lock);
+ return ERR_PTR(-EAGAIN);
+ }
+
+ /* now try to find a sighand */
+ if (likely(tsk->sighand)) {
+ sighand = tsk->sighand;
+ } else {
+ sighand = ERR_PTR(-ESRCH);
+ /*
+ * tsk is exiting; try to find another thread in the group
+ * whose sighand pointer is still alive.
+ */
+ list_for_each_entry_rcu(p, &tsk->thread_group, thread_group) {
+ if (p->sighand) {
+ sighand = tsk->sighand;
+ break;
+ }
+ }
+ }
+ /* prevent sighand from vanishing before we let go of tasklist_lock */
+ if (likely(sighand))
+ atomic_inc(&sighand->count);
+
+ /* done searching. */
+ read_unlock(&tasklist_lock);
+
+ if (likely(sighand))
+ down_write(&sighand->threadgroup_fork_lock);
+ return sighand;
+}
+
+/**
+ * threadgroup_fork_lock - let threadgroup resume CLONE_THREAD forks.
+ * @sighand: the threadgroup's sighand that threadgroup_fork_lock gave back
+ *
+ * Lets go of the threadgroup_fork_lock, and drops the sighand reference.
+ */
+void threadgroup_fork_unlock(struct sighand_struct *sighand)
+{
+ up_write(&sighand->threadgroup_fork_lock);
+ __cleanup_sighand(sighand);
+}
+
+/**
* cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
* @cgrp: the cgroup the task is attaching to
* @tsk: the task to be attached
@@ -3713,8 +3778,10 @@ static const struct file_operations
proc_cgroupstats_operations = {
* At the point that cgroup_fork() is called, 'current' is the parent
* task, and the passed argument 'child' points to the child task.
*/
-void cgroup_fork(struct task_struct *child)
+void cgroup_fork(struct task_struct *child, unsigned long clone_flags)
{
+ if (clone_flags & CLONE_THREAD)
+ down_read(¤t->sighand->threadgroup_fork_lock);
task_lock(current);
child->cgroups = current->cgroups;
get_css_set(child->cgroups);
@@ -3756,7 +3823,7 @@ void cgroup_fork_callbacks(struct task_struct *child)
* with the first call to cgroup_iter_start() - to guarantee that the
* new task ends up on its list.
*/
-void cgroup_post_fork(struct task_struct *child)
+void cgroup_post_fork(struct task_struct *child, unsigned long clone_flags)
{
if (use_task_css_set_links) {
write_lock(&css_set_lock);
@@ -3766,6 +3833,8 @@ void cgroup_post_fork(struct task_struct *child)
task_unlock(child);
write_unlock(&css_set_lock);
}
+ if (clone_flags & CLONE_THREAD)
+ up_read(¤t->sighand->threadgroup_fork_lock);
}
/**
* cgroup_exit - detach cgroup from exiting task
@@ -3841,6 +3910,26 @@ void cgroup_exit(struct task_struct *tsk, int
run_callbacks)
}
/**
+ * cgroup_fork_failed - undo operations for fork failure
+ * @tsk: pointer to task_struct of exiting process
+ * @run_callback: run exit callbacks?
+ *
+ * Description: Undo cgroup operations after cgroup_fork in fork failure.
+ *
+ * We release the read lock that was taken in cgroup_fork(), since it is
+ * supposed to be dropped in cgroup_post_fork in the success case. The other
+ * thing that wants to be done is detaching the failed child task from the
+ * cgroup, so we wrap cgroup_exit.
+ */
+void cgroup_fork_failed(struct task_struct *tsk, int run_callbacks,
+ unsigned long clone_flags)
+{
+ if (clone_flags & CLONE_THREAD)
+ up_read(¤t->sighand->threadgroup_fork_lock);
+ cgroup_exit(tsk, run_callbacks);
+}
+
+/**
* cgroup_clone - clone the cgroup the given subsystem is attached to
* @tsk: the task to be moved
* @subsys: the given subsystem
diff --git a/kernel/fork.c b/kernel/fork.c
index 404e6ca..daf5967 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -809,6 +809,9 @@ static int copy_sighand(unsigned long clone_flags, struct
task_struct *tsk)
return -ENOMEM;
atomic_set(&sig->count, 1);
memcpy(sig->action, current->sighand->action, sizeof(sig->action));
+#ifdef CONFIG_CGROUPS
+ init_rwsem(&sig->threadgroup_fork_lock);
+#endif
return 0;
}
@@ -1091,7 +1094,7 @@ static struct task_struct *copy_process(unsigned long
clone_flags,
monotonic_to_bootbased(&p->real_start_time);
p->io_context = NULL;
p->audit_context = NULL;
- cgroup_fork(p);
+ cgroup_fork(p, clone_flags);
#ifdef CONFIG_NUMA
p->mempolicy = mpol_dup(p->mempolicy);
if (IS_ERR(p->mempolicy)) {
@@ -1316,7 +1319,7 @@ static struct task_struct *copy_process(unsigned long
clone_flags,
spin_unlock(¤t->sighand->siglock);
write_unlock_irq(&tasklist_lock);
proc_fork_connector(p);
- cgroup_post_fork(p);
+ cgroup_post_fork(p, clone_flags);
perf_event_fork(p);
return p;
@@ -1350,7 +1353,7 @@ bad_fork_cleanup_policy:
mpol_put(p->mempolicy);
bad_fork_cleanup_cgroup:
#endif
- cgroup_exit(p, cgroup_callbacks_done);
+ cgroup_fork_failed(p, cgroup_callbacks_done, clone_flags);
delayacct_tsk_free(p);
module_put(task_thread_info(p)->exec_domain->module);
bad_fork_cleanup_count:
_______________________________________________
Containers mailing list
contain...@lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/containers
_______________________________________________
Devel mailing list
Devel@openvz.org
https://openvz.org/mailman/listinfo/devel
