On Sun, Dec 26, 2010 at 07:09:19AM -0500, Ben Blum wrote: > On Fri, Dec 24, 2010 at 03:22:26AM -0500, Ben Blum wrote: > > On Wed, Aug 11, 2010 at 01:46:04AM -0400, Ben Blum wrote: > > > On Fri, Jul 30, 2010 at 07:56:49PM -0400, Ben Blum wrote: > > > > This patch series is a revision of http://lkml.org/lkml/2010/6/25/11 . > > > > > > > > This patch series implements a write function for the 'cgroup.procs' > > > > per-cgroup file, which enables atomic movement of multithreaded > > > > applications between cgroups. Writing the thread-ID of any thread in a > > > > threadgroup to a cgroup's procs file causes all threads in the group to > > > > be moved to that cgroup safely with respect to threads forking/exiting. > > > > (Possible usage scenario: If running a multithreaded build system that > > > > sucks up system resources, this lets you restrict it all at once into a > > > > new cgroup to keep it under control.) > > > > > > > > Example: Suppose pid 31337 clones new threads 31338 and 31339. > > > > > > > > # cat /dev/cgroup/tasks > > > > ... > > > > 31337 > > > > 31338 > > > > 31339 > > > > # mkdir /dev/cgroup/foo > > > > # echo 31337 > /dev/cgroup/foo/cgroup.procs > > > > # cat /dev/cgroup/foo/tasks > > > > 31337 > > > > 31338 > > > > 31339 > > > > > > > > A new lock, called threadgroup_fork_lock and living in signal_struct, is > > > > introduced to ensure atomicity when moving threads between cgroups. It's > > > > taken for writing during the operation, and taking for reading in fork() > > > > around the calls to cgroup_fork() and cgroup_post_fork(). > > Well this time everything here is actually safe and correct, as far as > my best efforts and keen eyes can tell. I dropped the per_thread call > from the last series in favour of revising the subsystem callback > interface. It now looks like this: > > ss->can_attach() > - Thread-independent, possibly expensive/sleeping. > > ss->can_attach_task() > - Called per-thread, run with rcu_read so must not sleep. > > ss->pre_attach() > - Thread independent, must be atomic, happens before attach_task. > > ss->attach_task() > - Called per-thread, run with tasklist_lock so must not sleep. > > ss->attach() > - Thread independent, possibly expensive/sleeping, called last. Okay, so. I've revamped the cgroup_attach_proc implementation a bunch and this version should be a lot easier on the eyes (and brains). Issues that are addressed: 1) cgroup_attach_proc now iterates over leader->thread_group once, at the very beginning, and puts each task_struct that we want to move into an array, using get_task_struct to make sure they stick around. - threadgroup_fork_lock ensures no threads not in the array can appear, and allows us to use signal->nr_threads to determine the size of the array when kmallocing it. - This simplifies the rest of the function a bunch, since now we never need to do rcu_read_lock after building the array. All the subsystem callbacks are the same as described just above, but the "can't sleep" restriction is gone, so it's nice and clean. - Checking for a race with de_thread (the manoeuvre I refer to as "double-double-toil-and-trouble-check locking") now needs to be done only once, at the beginning (before building the array). 2) The nodemask allocation problem in cpuset is fixed the same way as before - the masks are shared between the three attach callbacks, so are made as static global variables. 3) The introduction of threadgroup_fork_lock in sched.h (specifically, in signal_struct) requires rwsem.h; the new include appears in the first patch. (An alternate plan would be to make it a struct pointer with an incomplete forward declaration and kmalloc/kfree it during housekeeping, but adding an include seems better than that particular complication.) In light of this, the definitions for threadgroup_fork_{read,write}_{un,}lock are also in sched.h. -- Ben --- Documentation/cgroups/cgroups.txt | 39 ++- block/blk-cgroup.c | 18 - include/linux/cgroup.h | 10 include/linux/init_task.h | 9 include/linux/sched.h | 37 +++ kernel/cgroup.c | 454 +++++++++++++++++++++++++++++++++----- kernel/cgroup_freezer.c | 26 -- kernel/cpuset.c | 105 +++----- kernel/fork.c | 10 kernel/ns_cgroup.c | 23 - kernel/sched.c | 38 --- mm/memcontrol.c | 18 - security/device_cgroup.c | 3 13 files changed, 575 insertions(+), 215 deletions(-) _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
