cgroups: read-write lock CLONE_THREAD forking per threadgroup

Adds functionality to read/write lock CLONE_THREAD fork()ing per-threadgroup

Add an rwsem that lives in a threadgroup's signal_struct that's taken for
reading in the fork path, under CONFIG_CGROUPS.  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.

This is a pre-patch for cgroup-procs-write.patch.

Signed-off-by: Ben Blum <bblum@andrew.cmu.edu>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Reviewed-by: Paul Menage <menage@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 8e7e135d0817..1fa9d940e301 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -957,6 +957,10 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
         tty_audit_fork(sig);
         sched_autogroup_fork(sig);
 
+#ifdef CONFIG_CGROUPS
+        init_rwsem(&sig->threadgroup_fork_lock);
+#endif
+
         sig->oom_adj = current->signal->oom_adj;
         sig->oom_score_adj = current->signal->oom_score_adj;
         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
@@ -1138,6 +1142,8 @@ 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;
+        if (clone_flags & CLONE_THREAD)
+                threadgroup_fork_read_lock(current);
         cgroup_fork(p);
 #ifdef CONFIG_NUMA
         p->mempolicy = mpol_dup(p->mempolicy);
@@ -1342,6 +1348,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         write_unlock_irq(&tasklist_lock);
         proc_fork_connector(p);
         cgroup_post_fork(p);
+        if (clone_flags & CLONE_THREAD)
+                threadgroup_fork_read_unlock(current);
         perf_event_fork(p);
         return p;
 
@@ -1380,6 +1388,8 @@ bad_fork_cleanup_policy:
         mpol_put(p->mempolicy);
 bad_fork_cleanup_cgroup:
 #endif
+        if (clone_flags & CLONE_THREAD)
+                threadgroup_fork_read_unlock(current);
         cgroup_exit(p, cgroup_callbacks_done);
         delayacct_tsk_free(p);
         module_put(task_thread_info(p)->exec_domain->module);