On Fri, 25 Jun 2010 01:46:54 -0400 Ben Blum <bblum@xxxxxxxxxxxxxx> wrote: > Adds functionality to read/write lock CLONE_THREAD fork()ing per-threadgroup > > From: Ben Blum <bblum@xxxxxxxxxxxxxx> > > This patch adds 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 cgroups-procs-write.patch. > Hmm, at adding a new lock, please describe its semantics. Following is my understanding, right ? Lock range: This rwsem is read-locked from cgroup_fork() to cgroup_post_fork(). Most of works for fork() are between cgroup_fork() and cgroup_post_for(). This means if sig->threadgroup_fork_lock is held, no new do_work() can make progress in this process groups. This rwsem is held only when CLONE_THREAD is in clone_flags. IOW, this rwsem is taken only at creating new thread. What we can do with this: By locking sig->threadgroup_fork_lock, a code can visit _all_ threads in a process group witout any races. So, if you want to implement an atomic operation against a process, taking this lock is an idea. For what: To implement an atomic process move in cgroup, we need this lock. Why this implemantation: Considering cgroup, threads in a cgroup can be under several different cgroup. So, we can't implement lock in cgroup-internal, we use signal struct. By the way, IMHO, hiding lock in cgroup_fork() and cgroup_post_fork() doesn't seem good idea. How about a code like this ? read_lock_thread_clone(current); cgroup_fork(); ..... cgroup_post_fork(); read_unlock_thrad_clone(current); We may have chances to move these lock to better position if cgroup is an only user. Thanks, -Kame _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
