user/sven/linux.git/kernel/sched, branch v4.2.4

sched/preempt: Fix cond_resched_lock() and cond_resched_softirq()

2015-10-22T21:49:35Z

commit fe32d3cd5e8eb0f82e459763374aa80797023403 upstream. These functions check should_resched() before unlocking spinlock/bh-enable: preempt_count always non-zero => should_resched() always returns false. cond_resched_lock() worked iff spin_needbreak is set. This patch adds argument "preempt_offset" to should_resched(). preempt_count offset constants for that: PREEMPT_DISABLE_OFFSET - offset after preempt_disable() PREEMPT_LOCK_OFFSET - offset after spin_lock() SOFTIRQ_DISABLE_OFFSET - offset after local_bh_distable() SOFTIRQ_LOCK_OFFSET - offset after spin_lock_bh() Signed-off-by: Konstantin Khlebnikov Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Graf Cc: Boris Ostrovsky Cc: David Vrabel Cc: Linus Torvalds Cc: Mike Galbraith Cc: Paul Mackerras Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: bdb438065890 ("sched: Extract the basic add/sub preempt_count modifiers") Link: http://lkml.kernel.org/r/20150715095204.12246.98268.stgit@buzz Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

sched/core: Fix TASK_DEAD race in finish_task_switch()

2015-10-22T21:49:19Z

commit 95913d97914f44db2b81271c2e2ebd4d2ac2df83 upstream. So the problem this patch is trying to address is as follows: CPU0 CPU1 context_switch(A, B) ttwu(A) LOCK A->pi_lock A->on_cpu == 0 finish_task_switch(A) prev_state = A->state <-. WMB | A->on_cpu = 0; | UNLOCK rq0->lock | | context_switch(C, A) `-- A->state = TASK_DEAD prev_state == TASK_DEAD put_task_struct(A) context_switch(A, C) finish_task_switch(A) A->state == TASK_DEAD put_task_struct(A) The argument being that the WMB will allow the load of A->state on CPU0 to cross over and observe CPU1's store of A->state, which will then result in a double-drop and use-after-free. Now the comment states (and this was true once upon a long time ago) that we need to observe A->state while holding rq->lock because that will order us against the wakeup; however the wakeup will not in fact acquire (that) rq->lock; it takes A->pi_lock these days. We can obviously fix this by upgrading the WMB to an MB, but that is expensive, so we'd rather avoid that. The alternative this patch takes is: smp_store_release(&A->on_cpu, 0), which avoids the MB on some archs, but not important ones like ARM. Reported-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Acked-by: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Cc: manfred@colorfullife.com Cc: will.deacon@arm.com Fixes: e4a52bcb9a18 ("sched: Remove rq->lock from the first half of ttwu()") Link: http://lkml.kernel.org/r/20150929124509.GG3816@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

sched: access local runqueue directly in single_task_running

2015-10-22T21:49:16Z

commit 00cc1633816de8c95f337608a1ea64e228faf771 upstream. Commit 2ee507c47293 ("sched: Add function single_task_running to let a task check if it is the only task running on a cpu") referenced the current runqueue with the smp_processor_id. When CONFIG_DEBUG_PREEMPT is enabled, that is only allowed if preemption is disabled or the currrent task is bound to the local cpu (e.g. kernel worker). With commit f78195129963 ("kvm: add halt_poll_ns module parameter") KVM calls single_task_running. If CONFIG_DEBUG_PREEMPT is enabled that generates a lot of kernel messages. To avoid adding preemption in that cases, as it would limit the usefulness, we change single_task_running to access directly the cpu local runqueue. Cc: Tim Chen Suggested-by: Peter Zijlstra Acked-by: Peter Zijlstra (Intel) Fixes: 2ee507c472939db4b146d545352b8a7c79ef47f8 Signed-off-by: Dominik Dingel Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman

sched: Fix cpu_active_mask/cpu_online_mask race

2015-09-21T17:10:45Z

commit dd9d3843755da95f63dd3a376f62b3e45c011210 upstream. There is a race condition in SMP bootup code, which may result in WARNING: CPU: 0 PID: 1 at kernel/workqueue.c:4418 workqueue_cpu_up_callback() or kernel BUG at kernel/smpboot.c:135! It can be triggered with a bit of luck in Linux guests running on busy hosts. CPU0 CPUn ==== ==== _cpu_up() __cpu_up() start_secondary() set_cpu_online() cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits)); cpu_notify(CPU_ONLINE) cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits)); During the various CPU_ONLINE callbacks CPUn is online but not active. Several things can go wrong at that point, depending on the scheduling of tasks on CPU0. Variant 1: cpu_notify(CPU_ONLINE) workqueue_cpu_up_callback() rebind_workers() set_cpus_allowed_ptr() This call fails because it requires an active CPU; rebind_workers() ends with a warning: WARNING: CPU: 0 PID: 1 at kernel/workqueue.c:4418 workqueue_cpu_up_callback() Variant 2: cpu_notify(CPU_ONLINE) smpboot_thread_call() smpboot_unpark_threads() .. __kthread_unpark() __kthread_bind() wake_up_state() .. select_task_rq() select_fallback_rq() The ->wake_cpu of the unparked thread is not allowed, making a call to select_fallback_rq() necessary. Then, select_fallback_rq() cannot find an allowed, active CPU and promptly resets the allowed CPUs, so that the task in question ends up on CPU0. When those unparked tasks are eventually executed, they run immediately into a BUG: kernel BUG at kernel/smpboot.c:135! Just changing the order in which the online/active bits are set (and adding some memory barriers), would solve the two issues above. However, it would change the order of operations back to the one before commit 6acbfb96976f ("sched: Fix hotplug vs. set_cpus_allowed_ptr()"), thus, reintroducing that particular problem. Going further back into history, we have at least the following commits touching this topic: - commit 2baab4e90495 ("sched: Fix select_fallback_rq() vs cpu_active/cpu_online") - commit 5fbd036b552f ("sched: Cleanup cpu_active madness") Together, these give us the following non-working solutions: - secondary CPU sets active before online, because active is assumed to be a subset of online; - secondary CPU sets online before active, because the primary CPU assumes that an online CPU is also active; - secondary CPU sets online and waits for primary CPU to set active, because it might deadlock. Commit 875ebe940d77 ("powerpc/smp: Wait until secondaries are active & online") introduces an arch-specific solution to this arch-independent problem. Now, go for a more general solution without explicit waiting and simply set active twice: once on the secondary CPU after online was set and once on the primary CPU after online was seen. set_cpus_allowed_ptr()") Signed-off-by: Jan H. Schönherr Acked-by: Peter Zijlstra Cc: Anton Blanchard Cc: Borislav Petkov Cc: Joerg Roedel Cc: Linus Torvalds Cc: Matt Wilson Cc: Michael Ellerman Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 6acbfb96976f ("sched: Fix hotplug vs. set_cpus_allowed_ptr()") Link: http://lkml.kernel.org/r/1439408156-18840-1-git-send-email-jschoenh@amazon.de Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

sched/fair: Test list head instead of list entry in throttle_cfs_rq()

2015-07-06T12:15:08Z

According to the comments, we need to test if this is the first throttled task, however, list_empty() tests on the entry cfs_rq->throttled_list, not the head, this is wrong. This is a bug because we don't re-init the list entry after removing it from the list, so list_empty() could return false even if the list is really empty. Signed-off-by: Cong Wang Signed-off-by: Cong Wang Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Ben Segall Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1435174907-432-1-git-send-email-xiyou.wangcong@gmail.com Signed-off-by: Ingo Molnar

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2015-07-04T18:29:59Z

Pull kvm fixes from Paolo Bonzini: "Except for the preempt notifiers fix, these are all small bugfixes that could have been waited for -rc2. Sending them now since I was taking care of Peter's patch anyway" * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: kvm: add hyper-v crash msrs values KVM: x86: remove data variable from kvm_get_msr_common KVM: s390: virtio-ccw: don't overwrite config space values KVM: x86: keep track of LVT0 changes under APICv KVM: x86: properly restore LVT0 KVM: x86: make vapics_in_nmi_mode atomic sched, preempt_notifier: separate notifier registration from static_key inc/dec

Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2015-07-04T15:56:53Z

Pull scheduler fixes from Ingo Molnar: "Debug info and other statistics fixes and related enhancements" * 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched/numa: Fix numa balancing stats in /proc/pid/sched sched/numa: Show numa_group ID in /proc/sched_debug task listings sched/debug: Move print_cfs_rq() declaration to kernel/sched/sched.h sched/stat: Expose /proc/pid/schedstat if CONFIG_SCHED_INFO=y sched/stat: Simplify the sched_info accounting dependency

sched/numa: Fix numa balancing stats in /proc/pid/sched

2015-07-04T08:04:33Z

Commit 44dba3d5d6a1 ("sched: Refactor task_struct to use numa_faults instead of numa_* pointers") modified the way tsk->numa_faults stats are accounted. However that commit never touched show_numa_stats() that is displayed in /proc/pid/sched and thus the numbers displayed in /proc/pid/sched don't match the actual numbers. Fix it by making sure that /proc/pid/sched reflects the task fault numbers. Also add group fault stats too. Also couple of more modifications are added here: 1. Format changes: - Previously we would list two entries per node, one for private and one for shared. Also the home node info was listed in each entry. - Now preferred node, total_faults and current node are displayed separately. - Now there is one entry per node, that lists private,shared task and group faults. 2. Unit changes: - p->numa_pages_migrated was getting reset after every read of /proc/pid/sched. It's more useful to have absolute numbers since differential migrations between two accesses can be more easily calculated. Signed-off-by: Srikar Dronamraju Acked-by: Rik van Riel Cc: Iulia Manda Cc: Linus Torvalds Cc: Mel Gorman Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1435252903-1081-4-git-send-email-srikar@linux.vnet.ibm.com Signed-off-by: Ingo Molnar

sched/numa: Show numa_group ID in /proc/sched_debug task listings

2015-07-04T08:04:32Z

Having the numa group ID in /proc/sched_debug helps to see how the numa groups have spread across the system. Signed-off-by: Srikar Dronamraju Acked-by: Rik van Riel Cc: Iulia Manda Cc: Linus Torvalds Cc: Mel Gorman Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1435252903-1081-3-git-send-email-srikar@linux.vnet.ibm.com Signed-off-by: Ingo Molnar

sched/debug: Move print_cfs_rq() declaration to kernel/sched/sched.h

2015-07-04T08:04:31Z

Currently print_cfs_rq() is declared in include/linux/sched.h. However it's not used outside kernel/sched. Hence move the declaration to kernel/sched/sched.h Also some functions are only available for CONFIG_SCHED_DEBUG=y. Hence move the declarations to within the #ifdef. Signed-off-by: Srikar Dronamraju Acked-by: Rik van Riel Cc: Iulia Manda Cc: Linus Torvalds Cc: Mel Gorman Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1435252903-1081-2-git-send-email-srikar@linux.vnet.ibm.com Signed-off-by: Ingo Molnar