user/sven/linux.git/kernel, 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

clocksource: Fix abs() usage w/ 64bit values

2015-10-22T21:49:33Z

commit 67dfae0cd72fec5cd158b6e5fb1647b7dbe0834c upstream. This patch fixes one cases where abs() was being used with 64-bit nanosecond values, where the result may be capped at 32-bits. This potentially could cause watchdog false negatives on 32-bit systems, so this patch addresses the issue by using abs64(). Signed-off-by: John Stultz Cc: Prarit Bhargava Cc: Richard Cochran Cc: Ingo Molnar Link: http://lkml.kernel.org/r/1442279124-7309-2-git-send-email-john.stultz@linaro.org Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

genirq: Fix race in register_irq_proc()

2015-10-22T21:49:33Z

commit 95c2b17534654829db428f11bcf4297c059a2a7e upstream. Per-IRQ directories in procfs are created only when a handler is first added to the irqdesc, not when the irqdesc is created. In the case of a shared IRQ, multiple tasks can race to create a directory. This race condition seems to have been present forever, but is easier to hit with async probing. Signed-off-by: Ben Hutchings Link: http://lkml.kernel.org/r/1443266636.2004.2.camel@decadent.org.uk Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

Revert "sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem"

2015-10-22T21:49:19Z

commit 0c986253b939cc14c69d4adbe2b4121bdf4aa220 upstream. This reverts commit d59cfc09c32a2ae31f1c3bc2983a0cd79afb3f14. d59cfc09c32a ("sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem") and b5ba75b5fc0e ("cgroup: simplify threadgroup locking") changed how cgroup synchronizes against task fork and exits so that it uses global percpu_rwsem instead of per-process rwsem; unfortunately, the write [un]lock paths of percpu_rwsem always involve synchronize_rcu_expedited() which turned out to be too expensive. Improvements for percpu_rwsem are scheduled to be merged in the coming v4.4-rc1 merge window which alleviates this issue. For now, revert the two commits to restore per-process rwsem. They will be re-applied for the v4.4-rc1 merge window. Signed-off-by: Tejun Heo Link: http://lkml.kernel.org/g/55F8097A.7000206@de.ibm.com Reported-by: Christian Borntraeger Cc: Oleg Nesterov Cc: "Paul E. McKenney" Cc: Peter Zijlstra Cc: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman

Revert "cgroup: simplify threadgroup locking"

2015-10-22T21:49:19Z

commit f9f9e7b776142fb1c0782cade004cc8e0147a199 upstream. This reverts commit b5ba75b5fc0e8404e2c50cb68f39bb6a53fc916f. d59cfc09c32a ("sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem") and b5ba75b5fc0e ("cgroup: simplify threadgroup locking") changed how cgroup synchronizes against task fork and exits so that it uses global percpu_rwsem instead of per-process rwsem; unfortunately, the write [un]lock paths of percpu_rwsem always involve synchronize_rcu_expedited() which turned out to be too expensive. Improvements for percpu_rwsem are scheduled to be merged in the coming v4.4-rc1 merge window which alleviates this issue. For now, revert the two commits to restore per-process rwsem. They will be re-applied for the v4.4-rc1 merge window. Signed-off-by: Tejun Heo Link: http://lkml.kernel.org/g/55F8097A.7000206@de.ibm.com Reported-by: Christian Borntraeger Cc: Oleg Nesterov Cc: "Paul E. McKenney" Cc: Peter Zijlstra Cc: Paolo Bonzini 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

locking/qspinlock/x86: Fix performance regression under unaccelerated VMs

2015-10-22T21:49:15Z

commit 43b3f02899f74ae9914a39547cc5492156f0027a upstream. Dave ran into horrible performance on a VM without PARAVIRT_SPINLOCKS set and Linus noted that the test-and-set implementation was retarded. One should spin on the variable with a load, not a RMW. While there, remove 'queued' from the name, as the lock isn't queued at all, but a simple test-and-set. Suggested-by: Linus Torvalds Reported-by: Dave Chinner Tested-by: Dave Chinner Signed-off-by: Peter Zijlstra (Intel) Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Waiman Long Link: http://lkml.kernel.org/r/20150904152523.GR18673@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

time: Fix timekeeping_freqadjust()'s incorrect use of abs() instead of abs64()

2015-10-22T21:49:14Z

commit 2619d7e9c92d524cb155ec89fd72875321512e5b upstream. The internal clocksteering done for fine-grained error correction uses a logarithmic approximation, so any time adjtimex() adjusts the clock steering, timekeeping_freqadjust() quickly approximates the correct clock frequency over a series of ticks. Unfortunately, the logic in timekeeping_freqadjust(), introduced in commit: dc491596f639 ("timekeeping: Rework frequency adjustments to work better w/ nohz") used the abs() function with a s64 error value to calculate the size of the approximated adjustment to be made. Per include/linux/kernel.h: "abs() should not be used for 64-bit types (s64, u64, long long) - use abs64()". Thus on 32-bit platforms, this resulted in the clocksteering to take a quite dampended random walk trying to converge on the proper frequency, which caused the adjustments to be made much slower then intended (most easily observed when large adjustments are made). This patch fixes the issue by using abs64() instead. Reported-by: Nuno Gonçalves Tested-by: Nuno Goncalves Signed-off-by: John Stultz Cc: Linus Torvalds Cc: Miroslav Lichvar Cc: Peter Zijlstra Cc: Prarit Bhargava Cc: Richard Cochran Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1441840051-20244-1-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

workqueue: Make flush_workqueue() available again to non GPL modules

2015-09-29T17:33:32Z

commit 1dadafa86a779884f14a6e7a3ddde1a57b0a0a65 upstream. Commit 37b1ef31a568fc02e53587620226e5f3c66454c8 ("workqueue: move flush_scheduled_work() to workqueue.h") moved the exported non GPL flush_scheduled_work() from a function to an inline wrapper. Unfortunately, it directly calls flush_workqueue() which is a GPL function. This has the effect of changing the licensing requirement for this function and makes it unavailable to non GPL modules. See commit ad7b1f841f8a54c6d61ff181451f55b68175e15a ("workqueue: Make schedule_work() available again to non GPL modules") for precedent. Signed-off-by: Tim Gardner Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman