user/sven/linux.git/include/linux/workqueue.h, branch v3.12.41

workqueue: fix hang involving racing cancel[_delayed]_work_sync()'s for PREEMPT_NONE

2015-04-09T11:14:05Z

commit 8603e1b30027f943cc9c1eef2b291d42c3347af1 upstream. cancel[_delayed]_work_sync() are implemented using __cancel_work_timer() which grabs the PENDING bit using try_to_grab_pending() and then flushes the work item with PENDING set to prevent the on-going execution of the work item from requeueing itself. try_to_grab_pending() can always grab PENDING bit without blocking except when someone else is doing the above flushing during cancelation. In that case, try_to_grab_pending() returns -ENOENT. In this case, __cancel_work_timer() currently invokes flush_work(). The assumption is that the completion of the work item is what the other canceling task would be waiting for too and thus waiting for the same condition and retrying should allow forward progress without excessive busy looping Unfortunately, this doesn't work if preemption is disabled or the latter task has real time priority. Let's say task A just got woken up from flush_work() by the completion of the target work item. If, before task A starts executing, task B gets scheduled and invokes __cancel_work_timer() on the same work item, its try_to_grab_pending() will return -ENOENT as the work item is still being canceled by task A and flush_work() will also immediately return false as the work item is no longer executing. This puts task B in a busy loop possibly preventing task A from executing and clearing the canceling state on the work item leading to a hang. task A task B worker executing work __cancel_work_timer() try_to_grab_pending() set work CANCELING flush_work() block for work completion completion, wakes up A __cancel_work_timer() while (forever) { try_to_grab_pending() -ENOENT as work is being canceled flush_work() false as work is no longer executing } This patch removes the possible hang by updating __cancel_work_timer() to explicitly wait for clearing of CANCELING rather than invoking flush_work() after try_to_grab_pending() fails with -ENOENT. Link: http://lkml.kernel.org/g/20150206171156.GA8942@axis.com v3: bit_waitqueue() can't be used for work items defined in vmalloc area. Switched to custom wake function which matches the target work item and exclusive wait and wakeup. v2: v1 used wake_up() on bit_waitqueue() which leads to NULL deref if the target bit waitqueue has wait_bit_queue's on it. Use DEFINE_WAIT_BIT() and __wake_up_bit() instead. Reported by Tomeu Vizoso. Signed-off-by: Tejun Heo Reported-by: Rabin Vincent Cc: Tomeu Vizoso Tested-by: Jesper Nilsson Tested-by: Rabin Vincent Signed-off-by: Jiri Slaby

workqueue: apply __WQ_ORDERED to create_singlethread_workqueue()

2014-10-13T13:41:19Z

commit e09c2c295468476a239d13324ce9042ec4de05eb upstream. create_singlethread_workqueue() is a compat interface for single threaded workqueue which maps to ordered workqueue w/ rescuer in the current implementation. create_singlethread_workqueue() currently implemented by invoking alloc_workqueue() w/ appropriate parameters. 8719dceae2f9 ("workqueue: reject adjusting max_active or applying attrs to ordered workqueues") introduced __WQ_ORDERED to protect ordered workqueues against dynamic attribute changes which can break ordering guarantees but forgot to apply it to create_singlethread_workqueue(). This in itself is okay as nobody currently uses dynamic attribute change on workqueues created with create_singlethread_workqueue(). However, 4c16bd327c ("workqueue: implement NUMA affinity for unbound workqueues") broke singlethreaded guarantee for ordered workqueues through allocating a separate pool_workqueue on each NUMA node by default. A later change 8a2b75384444 ("workqueue: fix ordered workqueues in NUMA setups") fixed it by allocating only one global pool_workqueue if __WQ_ORDERED is set. Combined, the __WQ_ORDERED omission in create_singlethread_workqueue() became critical breaking its single threadedness and ordering guarantee. Let's make create_singlethread_workqueue() wrap alloc_ordered_workqueue() instead so that it inherits __WQ_ORDERED and can implicitly track future ordered_workqueue changes. v2: I missed that __WQ_ORDERED now protects against pwq splitting across NUMA nodes and incorrectly described the patch as a nice-to-have fix to protect against future dynamic attribute usages. Oleg pointed out that this is actually a critical breakage due to 8a2b75384444 ("workqueue: fix ordered workqueues in NUMA setups"). Signed-off-by: Tejun Heo Reported-by: Mike Anderson Cc: Oleg Nesterov Cc: Gustavo Luiz Duarte Cc: Tomas Henzl Fixes: 4c16bd327c ("workqueue: implement NUMA affinity for unbound workqueues") Signed-off-by: Jiri Slaby

workqueue: mark WQ_NON_REENTRANT deprecated

2013-07-30T12:30:16Z

dbf2576e37 ("workqueue: make all workqueues non-reentrant") made WQ_NON_REENTRANT no-op but the following patches didn't remove the flag or update the documentation. Let's mark the flag deprecated and update the documentation accordingly. Signed-off-by: Tejun Heo

drivers: avoid format strings in names passed to alloc_workqueue()

2013-07-03T23:07:41Z

For the workqueue creation interfaces that do not expect format strings, make sure they cannot accidently be parsed that way. Additionally, clean up calls made with a single parameter that would be handled as a format string. Many callers are passing potentially dynamic string content, so use "%s" in those cases to avoid any potential accidents. Signed-off-by: Kees Cook Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

workqueue: Add system wide power_efficient workqueues

2013-05-14T17:50:06Z

This patch adds system wide workqueues aligned towards power saving. This is done by allocating them with WQ_UNBOUND flag if 'wq_power_efficient' is set to 'true'. tj: updated comments a bit. Signed-off-by: Viresh Kumar Signed-off-by: Tejun Heo

workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues

2013-05-14T17:50:06Z

Workqueues can be performance or power-oriented. Currently, most workqueues are bound to the CPU they were created on. This gives good performance (due to cache effects) at the cost of potentially waking up otherwise idle cores (Idle from scheduler's perspective. Which may or may not be physically idle) just to process some work. To save power, we can allow the work to be rescheduled on a core that is already awake. Workqueues created with the WQ_UNBOUND flag will allow some power savings. However, we don't change the default behaviour of the system. To enable power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to be turned on. This option can also be overridden by the workqueue.power_efficient boot parameter. tj: Updated config description and comments. Renamed CONFIG_WQ_POWER_EFFICIENT to CONFIG_WQ_POWER_EFFICIENT_DEFAULT. Signed-off-by: Viresh Kumar Reviewed-by: Amit Kucheria Signed-off-by: Tejun Heo

workqueue: include workqueue info when printing debug dump of a worker task

2013-05-01T00:04:02Z

One of the problems that arise when converting dedicated custom threadpool to workqueue is that the shared worker pool used by workqueue anonimizes each worker making it more difficult to identify what the worker was doing on which target from the output of sysrq-t or debug dump from oops, BUG() and friends. This patch implements set_worker_desc() which can be called from any workqueue work function to set its description. When the worker task is dumped for whatever reason - sysrq-t, WARN, BUG, oops, lockdep assertion and so on - the description will be printed out together with the workqueue name and the worker function pointer. The printing side is implemented by print_worker_info() which is called from functions in task dump paths - sched_show_task() and dump_stack_print_info(). print_worker_info() can be safely called on any task in any state as long as the task struct itself is accessible. It uses probe_*() functions to access worker fields. It may print garbage if something went very wrong, but it wouldn't cause (another) oops. The description is currently limited to 24bytes including the terminating \0. worker->desc_valid and workder->desc[] are added and the 64 bytes marker which was already incorrect before adding the new fields is moved to the correct position. Here's an example dump with writeback updated to set the bdi name as worker desc. Hardware name: Bochs Modules linked in: Pid: 7, comm: kworker/u9:0 Not tainted 3.9.0-rc1-work+ #1 Workqueue: writeback bdi_writeback_workfn (flush-8:0) ffffffff820a3ab0 ffff88000f6e9cb8 ffffffff81c61845 ffff88000f6e9cf8 ffffffff8108f50f 0000000000000000 0000000000000000 ffff88000cde16b0 ffff88000cde1aa8 ffff88001ee19240 ffff88000f6e9fd8 ffff88000f6e9d08 Call Trace: [] dump_stack+0x19/0x1b [] warn_slowpath_common+0x7f/0xc0 [] warn_slowpath_null+0x1a/0x20 [] bdi_writeback_workfn+0x2a0/0x3b0 ... Signed-off-by: Tejun Heo Cc: Peter Zijlstra Cc: Ingo Molnar Acked-by: Jan Kara Cc: Oleg Nesterov Cc: Jens Axboe Cc: Dave Chinner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

workqueue: update sysfs interface to reflect NUMA awareness and a kernel param to disable NUMA affinity

2013-04-01T18:23:38Z

Unbound workqueues are now NUMA aware. Let's add some control knobs and update sysfs interface accordingly. * Add kernel param workqueue.numa_disable which disables NUMA affinity globally. * Replace sysfs file "pool_id" with "pool_ids" which contain node:pool_id pairs. This change is userland-visible but "pool_id" hasn't seen a release yet, so this is okay. * Add a new sysf files "numa" which can toggle NUMA affinity on individual workqueues. This is implemented as attrs->no_numa whichn is special in that it isn't part of a pool's attributes. It only affects how apply_workqueue_attrs() picks which pools to use. After "pool_ids" change, first_pwq() doesn't have any user left. Removed. Signed-off-by: Tejun Heo Reviewed-by: Lai Jiangshan

workqueue: inline trivial wrappers

2013-03-13T23:51:36Z

There's no reason to make these trivial wrappers full (exported) functions. Inline the followings. queue_work() queue_delayed_work() mod_delayed_work() schedule_work_on() schedule_work() schedule_delayed_work_on() schedule_delayed_work() keventd_up() Signed-off-by: Tejun Heo

workqueue: implement current_is_workqueue_rescuer()

2013-03-13T00:42:01Z

Implement a function which queries whether it currently is running off a workqueue rescuer. This will be used to convert writeback to workqueue. Signed-off-by: Tejun Heo