linux/kernel/cpuset.c, branch v4.5

cpuset: make mm migration asynchronous

2016-01-22T15:22:46Z

If "cpuset.memory_migrate" is set, when a process is moved from one cpuset to another with a different memory node mask, pages in used by the process are migrated to the new set of nodes. This was performed synchronously in the ->attach() callback, which is synchronized against process management. Recently, the synchronization was changed from per-process rwsem to global percpu rwsem for simplicity and optimization. Combined with the synchronous mm migration, this led to deadlocks because mm migration could schedule a work item which may in turn try to create a new worker blocking on the process management lock held from cgroup process migration path. This heavy an operation shouldn't be performed synchronously from that deep inside cgroup migration in the first place. This patch punts the actual migration to an ordered workqueue and updates cgroup process migration and cpuset config update paths to flush the workqueue after all locks are released. This way, the operations still seem synchronous to userland without entangling mm migration with process management synchronization. CPU hotplug can also invoke mm migration but there's no reason for it to wait for mm migrations and thus doesn't synchronize against their completions. Signed-off-by: Tejun Heo Reported-and-tested-by: Christian Borntraeger Cc: stable@vger.kernel.org # v4.4+

Merge branch 'for-4.4-fixes' into for-4.5

2015-12-03T15:22:52Z

cgroup: fix handling of multi-destination migration from subtree_control enabling

2015-12-03T15:18:21Z

Consider the following v2 hierarchy. P0 (+memory) --- P1 (-memory) --- A \- B P0 has memory enabled in its subtree_control while P1 doesn't. If both A and B contain processes, they would belong to the memory css of P1. Now if memory is enabled on P1's subtree_control, memory csses should be created on both A and B and A's processes should be moved to the former and B's processes the latter. IOW, enabling controllers can cause atomic migrations into different csses. The core cgroup migration logic has been updated accordingly but the controller migration methods haven't and still assume that all tasks migrate to a single target css; furthermore, the methods were fed the css in which subtree_control was updated which is the parent of the target csses. pids controller depends on the migration methods to move charges and this made the controller attribute charges to the wrong csses often triggering the following warning by driving a counter negative. WARNING: CPU: 1 PID: 1 at kernel/cgroup_pids.c:97 pids_cancel.constprop.6+0x31/0x40() Modules linked in: CPU: 1 PID: 1 Comm: systemd Not tainted 4.4.0-rc1+ #29 ... ffffffff81f65382 ffff88007c043b90 ffffffff81551ffc 0000000000000000 ffff88007c043bc8 ffffffff810de202 ffff88007a752000 ffff88007a29ab00 ffff88007c043c80 ffff88007a1d8400 0000000000000001 ffff88007c043bd8 Call Trace: [] dump_stack+0x4e/0x82 [] warn_slowpath_common+0x82/0xc0 [] warn_slowpath_null+0x1a/0x20 [] pids_cancel.constprop.6+0x31/0x40 [] pids_can_attach+0x6d/0xf0 [] cgroup_taskset_migrate+0x6c/0x330 [] cgroup_migrate+0xf5/0x190 [] cgroup_attach_task+0x176/0x200 [] __cgroup_procs_write+0x2ad/0x460 [] cgroup_procs_write+0x14/0x20 [] cgroup_file_write+0x35/0x1c0 [] kernfs_fop_write+0x141/0x190 [] __vfs_write+0x28/0xe0 [] vfs_write+0xac/0x1a0 [] SyS_write+0x49/0xb0 [] entry_SYSCALL_64_fastpath+0x12/0x76 This patch fixes the bug by removing @css parameter from the three migration methods, ->can_attach, ->cancel_attach() and ->attach() and updating cgroup_taskset iteration helpers also return the destination css in addition to the task being migrated. All controllers are updated accordingly. * Controllers which don't care whether there are one or multiple target csses can be converted trivially. cpu, io, freezer, perf, netclassid and netprio fall in this category. * cpuset's current implementation assumes that there's single source and destination and thus doesn't support v2 hierarchy already. The only change made by this patchset is how that single destination css is obtained. * memory migration path already doesn't do anything on v2. How the single destination css is obtained is updated and the prep stage of mem_cgroup_can_attach() is reordered to accomodate the change. * pids is the only controller which was affected by this bug. It now correctly handles multi-destination migrations and no longer causes counter underflow from incorrect accounting. Signed-off-by: Tejun Heo Reported-and-tested-by: Daniel Wagner Cc: Aleksa Sarai

cpuset: Replace all instances of time_t with time64_t

2015-11-25T19:00:05Z

The following patch replaces all instances of time_t with time64_t i.e. change the type used for representing time from 32-bit to 64-bit. All 32-bit kernels to date use a signed 32-bit time_t type, which can only represent time until January 2038. Since embedded systems running 32-bit Linux are going to survive beyond that date, we have to change all current uses, in a backwards compatible way. The patch also changes the function get_seconds() that returns a 32-bit integer to ktime_get_seconds() that returns seconds as 64-bit integer. The patch changes the type of ticks from time_t to u32. We keep ticks as 32-bits as the function uses 32-bit arithmetic which would prove less expensive than 64-bit arithmetic and the function is expected to be called atleast once every 32 seconds. Signed-off-by: Heena Sirwani Reviewed-by: Arnd Bergmann Signed-off-by: Arnd Bergmann Signed-off-by: Tejun Heo

Merge branch 'akpm' (patches from Andrew)

2015-11-06T07:10:54Z

Merge patch-bomb from Andrew Morton: - inotify tweaks - some ocfs2 updates (many more are awaiting review) - various misc bits - kernel/watchdog.c updates - Some of mm. I have a huge number of MM patches this time and quite a lot of it is quite difficult and much will be held over to next time. * emailed patches from Andrew Morton : (162 commits) selftests: vm: add tests for lock on fault mm: mlock: add mlock flags to enable VM_LOCKONFAULT usage mm: introduce VM_LOCKONFAULT mm: mlock: add new mlock system call mm: mlock: refactor mlock, munlock, and munlockall code kasan: always taint kernel on report mm, slub, kasan: enable user tracking by default with KASAN=y kasan: use IS_ALIGNED in memory_is_poisoned_8() kasan: Fix a type conversion error lib: test_kasan: add some testcases kasan: update reference to kasan prototype repo kasan: move KASAN_SANITIZE in arch/x86/boot/Makefile kasan: various fixes in documentation kasan: update log messages kasan: accurately determine the type of the bad access kasan: update reported bug types for kernel memory accesses kasan: update reported bug types for not user nor kernel memory accesses mm/kasan: prevent deadlock in kasan reporting mm/kasan: don't use kasan shadow pointer in generic functions mm/kasan: MODULE_VADDR is not available on all archs ...

mm, oom: remove task_lock protecting comm printing

2015-11-06T03:34:48Z

The oom killer takes task_lock() in a couple of places solely to protect printing the task's comm. A process's comm, including current's comm, may change due to /proc/pid/comm or PR_SET_NAME. The comm will always be NULL-terminated, so the worst race scenario would only be during update. We can tolerate a comm being printed that is in the middle of an update to avoid taking the lock. Other locations in the kernel have already dropped task_lock() when printing comm, so this is consistent. Signed-off-by: David Rientjes Suggested-by: Oleg Nesterov Cc: Michal Hocko Cc: Vladimir Davydov Cc: Sergey Senozhatsky Acked-by: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

cgroup: replace cgroup_has_tasks() with cgroup_is_populated()

2015-10-15T20:41:50Z

Currently, cgroup_has_tasks() tests whether the target cgroup has any css_set linked to it. This works because a css_set's refcnt converges with the number of tasks linked to it and thus there's no css_set linked to a cgroup if it doesn't have any live tasks. To help tracking resource usage of zombie tasks, putting the ref of css_set will be separated from disassociating the task from the css_set which means that a cgroup may have css_sets linked to it even when it doesn't have any live tasks. This patch replaces cgroup_has_tasks() with cgroup_is_populated() which tests cgroup->nr_populated instead which locally counts the number of populated css_sets. Unlike cgroup_has_tasks(), cgroup_is_populated() is recursive - if any of the descendants is populated, the cgroup is populated too. While this changes the meaning of the test, all the existing users are okay with the change. While at it, replace the open-coded ->populated_cnt test in cgroup_events_show() with cgroup_is_populated(). Signed-off-by: Tejun Heo Cc: Li Zefan Cc: Johannes Weiner Cc: Michal Hocko

cgroup, memcg, cpuset: implement cgroup_taskset_for_each_leader()

2015-09-22T16:46:53Z

It wasn't explicitly documented but, when a process is being migrated, cpuset and memcg depend on cgroup_taskset_first() returning the threadgroup leader; however, this approach is somewhat ghetto and would no longer work for the planned multi-process migration. This patch introduces explicit cgroup_taskset_for_each_leader() which iterates over only the threadgroup leaders and replaces cgroup_taskset_first() usages for accessing the leader with it. This prepares both memcg and cpuset for multi-process migration. This patch also updates the documentation for cgroup_taskset_for_each() to clarify the iteration rules and removes comments mentioning task ordering in tasksets. v2: A previous patch which added threadgroup leader test was dropped. Patch updated accordingly. Signed-off-by: Tejun Heo Acked-by: Zefan Li Acked-by: Michal Hocko Cc: Johannes Weiner

cpuset: migrate memory only for threadgroup leaders

2015-09-22T16:46:53Z

If memory_migrate flag is set, cpuset migrates memory according to the destnation css's nodemask. The current implementation migrates memory whenever any thread of a process is migrated making the behavior somewhat arbitrary. Let's tie memory operations to the threadgroup leader so that memory is migrated only when the leader is migrated. While this is a behavior change, given the inherent fuziness, this change is not too likely to be noticed and allows us to clearly define who owns the memory (always the leader) and helps the planned atomic multi-process migration. Note that we're currently migrating memory in migration path proper while holding all the locks. In the long term, this should be moved out to an async work item. Signed-off-by: Tejun Heo Acked-by: Zefan Li

cgroup: replace cftype->mode with CFTYPE_WORLD_WRITABLE

2015-09-18T21:54:23Z

cftype->mode allows controllers to give arbitrary permissions to interface knobs. Except for "cgroup.event_control", the existing uses are spurious. * Some explicitly specify S_IRUGO | S_IWUSR even though that's the default. * "cpuset.memory_pressure" specifies S_IRUGO while also setting a write callback which returns -EACCES. All it needs to do is simply not setting a write callback. "cgroup.event_control" uses cftype->mode to make the file world-writable. It's a misdesigned interface and we don't want controllers to be tweaking interface file permissions in general. This patch removes cftype->mode and all its spurious uses and implements CFTYPE_WORLD_WRITABLE for "cgroup.event_control" which is marked as compatibility-only. Signed-off-by: Tejun Heo Cc: Li Zefan Cc: Johannes Weiner