linux/kernel/sched, branch v3.10.34

sched: Fix double normalization of vruntime

2014-03-24T04:38:09Z

commit 791c9e0292671a3bfa95286bb5c08129d8605618 upstream. dequeue_entity() is called when p->on_rq and sets se->on_rq = 0 which appears to guarentee that the !se->on_rq condition is met. If the task has done set_current_state(TASK_INTERRUPTIBLE) without schedule() the second condition will be met and vruntime will be incorrectly adjusted twice. In certain cases this can result in the task's vruntime never increasing past the vruntime of other tasks on the CFS' run queue, starving them of CPU time. This patch changes switched_from_fair() to use !p->on_rq instead of !se->on_rq. I'm able to cause a task with a priority of 120 to starve all other tasks with the same priority on an ARM platform running 3.2.51-rt72 PREEMPT RT by writing one character at time to a serial tty (16550 UART) in a tight loop. I'm also able to verify making this change corrects the problem on that platform and kernel version. Signed-off-by: George McCollister Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1392767811-28916-1-git-send-email-george.mccollister@gmail.com Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

sched: Guarantee new group-entities always have weight

2014-01-15T23:28:54Z

commit 0ac9b1c21874d2490331233b3242085f8151e166 upstream. Currently, group entity load-weights are initialized to zero. This admits some races with respect to the first time they are re-weighted in earlty use. ( Let g[x] denote the se for "g" on cpu "x". ) Suppose that we have root->a and that a enters a throttled state, immediately followed by a[0]->t1 (the only task running on cpu[0]) blocking: put_prev_task(group_cfs_rq(a[0]), t1) put_prev_entity(..., t1) check_cfs_rq_runtime(group_cfs_rq(a[0])) throttle_cfs_rq(group_cfs_rq(a[0])) Then, before unthrottling occurs, let a[0]->b[0]->t2 wake for the first time: enqueue_task_fair(rq[0], t2) enqueue_entity(group_cfs_rq(b[0]), t2) enqueue_entity_load_avg(group_cfs_rq(b[0]), t2) account_entity_enqueue(group_cfs_ra(b[0]), t2) update_cfs_shares(group_cfs_rq(b[0])) < skipped because b is part of a throttled hierarchy > enqueue_entity(group_cfs_rq(a[0]), b[0]) ... We now have b[0] enqueued, yet group_cfs_rq(a[0])->load.weight == 0 which violates invariants in several code-paths. Eliminate the possibility of this by initializing group entity weight. Signed-off-by: Paul Turner Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20131016181627.22647.47543.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar Cc: Chris J Arges Signed-off-by: Greg Kroah-Hartman

sched: Fix hrtimer_cancel()/rq->lock deadlock

2014-01-15T23:28:54Z

commit 927b54fccbf04207ec92f669dce6806848cbec7d upstream. __start_cfs_bandwidth calls hrtimer_cancel while holding rq->lock, waiting for the hrtimer to finish. However, if sched_cfs_period_timer runs for another loop iteration, the hrtimer can attempt to take rq->lock, resulting in deadlock. Fix this by ensuring that cfs_b->timer_active is cleared only if the _latest_ call to do_sched_cfs_period_timer is returning as idle. Then __start_cfs_bandwidth can just call hrtimer_try_to_cancel and wait for that to succeed or timer_active == 1. Signed-off-by: Ben Segall Signed-off-by: Peter Zijlstra Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181622.22647.16643.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar Cc: Chris J Arges Signed-off-by: Greg Kroah-Hartman

sched: Fix cfs_bandwidth misuse of hrtimer_expires_remaining

2014-01-15T23:28:54Z

commit db06e78cc13d70f10877e0557becc88ab3ad2be8 upstream. hrtimer_expires_remaining does not take internal hrtimer locks and thus must be guarded against concurrent __hrtimer_start_range_ns (but returning HRTIMER_RESTART is safe). Use cfs_b->lock to make it safe. Signed-off-by: Ben Segall Signed-off-by: Peter Zijlstra Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181617.22647.73829.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar Cc: Chris J Arges Signed-off-by: Greg Kroah-Hartman

sched: Fix race on toggling cfs_bandwidth_used

2014-01-15T23:28:54Z

commit 1ee14e6c8cddeeb8a490d7b54cd9016e4bb900b4 upstream. When we transition cfs_bandwidth_used to false, any currently throttled groups will incorrectly return false from cfs_rq_throttled. While tg_set_cfs_bandwidth will unthrottle them eventually, currently running code (including at least dequeue_task_fair and distribute_cfs_runtime) will cause errors. Fix this by turning off cfs_bandwidth_used only after unthrottling all cfs_rqs. Tested: toggle bandwidth back and forth on a loaded cgroup. Caused crashes in minutes without the patch, hasn't crashed with it. Signed-off-by: Ben Segall Signed-off-by: Peter Zijlstra Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181611.22647.80365.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar Cc: Chris J Arges Signed-off-by: Greg Kroah-Hartman

sched: fix the theoretical signal_wake_up() vs schedule() race

2014-01-09T20:24:23Z

commit e0acd0a68ec7dbf6b7a81a87a867ebd7ac9b76c4 upstream. This is only theoretical, but after try_to_wake_up(p) was changed to check p->state under p->pi_lock the code like __set_current_state(TASK_INTERRUPTIBLE); schedule(); can miss a signal. This is the special case of wait-for-condition, it relies on try_to_wake_up/schedule interaction and thus it does not need mb() between __set_current_state() and if(signal_pending). However, this __set_current_state() can move into the critical section protected by rq->lock, now that try_to_wake_up() takes another lock we need to ensure that it can't be reordered with "if (signal_pending(current))" check inside that section. The patch is actually one-liner, it simply adds smp_wmb() before spin_lock_irq(rq->lock). This is what try_to_wake_up() already does by the same reason. We turn this wmb() into the new helper, smp_mb__before_spinlock(), for better documentation and to allow the architectures to change the default implementation. While at it, kill smp_mb__after_lock(), it has no callers. Perhaps we can also add smp_mb__before/after_spinunlock() for prepare_to_wait(). Signed-off-by: Oleg Nesterov Acked-by: Peter Zijlstra Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities

2014-01-09T20:24:21Z

commit 757dfcaa41844595964f1220f1d33182dae49976 upstream. This patch touches the RT group scheduling case. Functions inc_rt_prio_smp() and dec_rt_prio_smp() change (global) rq's priority, while rt_rq passed to them may be not the top-level rt_rq. This is wrong, because changing of priority on a child level does not guarantee that the priority is the highest all over the rq. So, this leak makes RT balancing unusable. The short example: the task having the highest priority among all rq's RT tasks (no one other task has the same priority) are waking on a throttle rt_rq. The rq's cpupri is set to the task's priority equivalent, but real rq->rt.highest_prio.curr is less. The patch below fixes the problem. Signed-off-by: Kirill Tkhai Signed-off-by: Peter Zijlstra CC: Steven Rostedt Link: http://lkml.kernel.org/r/49231385567953@web4m.yandex.ru Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

sched: numa: skip inaccessible VMAs

2014-01-09T20:24:21Z

commit 3c67f474558748b604e247d92b55dfe89654c81d upstream. Inaccessible VMA should not be trapping NUMA hint faults. Skip them. Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel Cc: Alex Thorlton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

sched: Avoid throttle_cfs_rq() racing with period_timer stopping

2013-12-20T15:45:11Z

commit f9f9ffc237dd924f048204e8799da74f9ecf40cf upstream. throttle_cfs_rq() doesn't check to make sure that period_timer is running, and while update_curr/assign_cfs_runtime does, a concurrently running period_timer on another cpu could cancel itself between this cpu's update_curr and throttle_cfs_rq(). If there are no other cfs_rqs running in the tg to restart the timer, this causes the cfs_rq to be stranded forever. Fix this by calling __start_cfs_bandwidth() in throttle if the timer is inactive. (Also add some sched_debug lines for cfs_bandwidth.) Tested: make a run/sleep task in a cgroup, loop switching the cgroup between 1ms/100ms quota and unlimited, checking for timer_active=0 and throttled=1 as a failure. With the throttle_cfs_rq() change commented out this fails, with the full patch it passes. Signed-off-by: Ben Segall Signed-off-by: Peter Zijlstra Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181632.22647.84174.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar Cc: Chris J Arges Signed-off-by: Greg Kroah-Hartman

sched/fair: Fix small race where child->se.parent,cfs_rq might point to invalid ones

2013-10-01T16:17:45Z

commit 6c9a27f5da9609fca46cb2b183724531b48f71ad upstream. There is a small race between copy_process() and cgroup_attach_task() where child->se.parent,cfs_rq points to invalid (old) ones. parent doing fork() | someone moving the parent to another cgroup -------------------------------+--------------------------------------------- copy_process() + dup_task_struct() -> parent->se is copied to child->se. se.parent,cfs_rq of them point to old ones. cgroup_attach_task() + cgroup_task_migrate() -> parent->cgroup is updated. + cpu_cgroup_attach() + sched_move_task() + task_move_group_fair() +- set_task_rq() -> se.parent,cfs_rq of parent are updated. + cgroup_fork() -> parent->cgroup is copied to child->cgroup. (*1) + sched_fork() + task_fork_fair() -> se.parent,cfs_rq of child are accessed while they point to old ones. (*2) In the worst case, this bug can lead to "use-after-free" and cause a panic, because it's new cgroup's refcount that is incremented at (*1), so the old cgroup(and related data) can be freed before (*2). In fact, a panic caused by this bug was originally caught in RHEL6.4. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [] sched_slice+0x6e/0xa0 [...] Call Trace: [] place_entity+0x75/0xa0 [] task_fork_fair+0xaa/0x160 [] sched_fork+0x6b/0x140 [] copy_process+0x5b2/0x1450 [] ? wake_up_new_task+0xd9/0x130 [] do_fork+0x94/0x460 [] ? sys_wait4+0xae/0x100 [] sys_clone+0x28/0x30 [] stub_clone+0x13/0x20 [] ? system_call_fastpath+0x16/0x1b Signed-off-by: Daisuke Nishimura Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/039601ceae06$733d3130$59b79390$@mxp.nes.nec.co.jp Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman