user/sven/linux.git/kernel/sched, branch v4.14.85

sched/core: Take the hotplug lock in sched_init_smp()

2018-11-27T15:10:49Z

[ Upstream commit 40fa3780bac2b654edf23f6b13f4e2dd550aea10 ] When running on linux-next (8c60c36d0b8c ("Add linux-next specific files for 20181019")) + CONFIG_PROVE_LOCKING=y on a big.LITTLE system (e.g. Juno or HiKey960), we get the following report: [ 0.748225] Call trace: [ 0.750685] lockdep_assert_cpus_held+0x30/0x40 [ 0.755236] static_key_enable_cpuslocked+0x20/0xc8 [ 0.760137] build_sched_domains+0x1034/0x1108 [ 0.764601] sched_init_domains+0x68/0x90 [ 0.768628] sched_init_smp+0x30/0x80 [ 0.772309] kernel_init_freeable+0x278/0x51c [ 0.776685] kernel_init+0x10/0x108 [ 0.780190] ret_from_fork+0x10/0x18 The static_key in question is 'sched_asym_cpucapacity' introduced by commit: df054e8445a4 ("sched/topology: Add static_key for asymmetric CPU capacity optimizations") In this particular case, we enable it because smp_prepare_cpus() will end up fetching the capacity-dmips-mhz entry from the devicetree, so we already have some asymmetry detected when entering sched_init_smp(). This didn't get detected in tip/sched/core because we were missing: commit cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations") Calls to build_sched_domains() post sched_init_smp() will hold the hotplug lock, it just so happens that this very first call is a special case. As stated by a comment in sched_init_smp(), "There's no userspace yet to cause hotplug operations" so this is a harmless warning. However, to both respect the semantics of underlying callees and make lockdep happy, take the hotplug lock in sched_init_smp(). This also satisfies the comment atop sched_init_domains() that says "Callers must hold the hotplug lock". Reported-by: Sudeep Holla Tested-by: Sudeep Holla Signed-off-by: Valentin Schneider Signed-off-by: Peter Zijlstra (Intel) Cc: Dietmar.Eggemann@arm.com Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: morten.rasmussen@arm.com Cc: quentin.perret@arm.com Link: http://lkml.kernel.org/r/1540301851-3048-1-git-send-email-valentin.schneider@arm.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin

sched/fair: Fix the min_vruntime update logic in dequeue_entity()

2018-11-13T19:14:50Z

[ Upstream commit 9845c49cc9bbb317a0bc9e9cf78d8e09d54c9af0 ] The comment and the code around the update_min_vruntime() call in dequeue_entity() are not in agreement. >From commit: b60205c7c558 ("sched/fair: Fix min_vruntime tracking") I think that we want to update min_vruntime when a task is sleeping/migrating. So, the check is inverted there - fix it. Signed-off-by: Song Muchun Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: b60205c7c558 ("sched/fair: Fix min_vruntime tracking") Link: http://lkml.kernel.org/r/20181014112612.2614-1-smuchun@gmail.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

sched/fair: Fix throttle_list starvation with low CFS quota

2018-11-10T15:48:36Z

commit baa9be4ffb55876923dc9716abc0a448e510ba30 upstream. With a very low cpu.cfs_quota_us setting, such as the minimum of 1000, distribute_cfs_runtime may not empty the throttled_list before it runs out of runtime to distribute. In that case, due to the change from c06f04c7048 to put throttled entries at the head of the list, later entries on the list will starve. Essentially, the same X processes will get pulled off the list, given CPU time and then, when expired, get put back on the head of the list where distribute_cfs_runtime will give runtime to the same set of processes leaving the rest. Fix the issue by setting a bit in struct cfs_bandwidth when distribute_cfs_runtime is running, so that the code in throttle_cfs_rq can decide to put the throttled entry on the tail or the head of the list. The bit is set/cleared by the callers of distribute_cfs_runtime while they hold cfs_bandwidth->lock. This is easy to reproduce with a handful of CPU consumers. I use 'crash' on the live system. In some cases you can simply look at the throttled list and see the later entries are not changing: crash> list cfs_rq.throttled_list -H 0xffff90b54f6ade40 -s cfs_rq.runtime_remaining | paste - - | awk '{print $1" "$4}' | pr -t -n3 1 ffff90b56cb2d200 -976050 2 ffff90b56cb2cc00 -484925 3 ffff90b56cb2bc00 -658814 4 ffff90b56cb2ba00 -275365 5 ffff90b166a45600 -135138 6 ffff90b56cb2da00 -282505 7 ffff90b56cb2e000 -148065 8 ffff90b56cb2fa00 -872591 9 ffff90b56cb2c000 -84687 10 ffff90b56cb2f000 -87237 11 ffff90b166a40a00 -164582 crash> list cfs_rq.throttled_list -H 0xffff90b54f6ade40 -s cfs_rq.runtime_remaining | paste - - | awk '{print $1" "$4}' | pr -t -n3 1 ffff90b56cb2d200 -994147 2 ffff90b56cb2cc00 -306051 3 ffff90b56cb2bc00 -961321 4 ffff90b56cb2ba00 -24490 5 ffff90b166a45600 -135138 6 ffff90b56cb2da00 -282505 7 ffff90b56cb2e000 -148065 8 ffff90b56cb2fa00 -872591 9 ffff90b56cb2c000 -84687 10 ffff90b56cb2f000 -87237 11 ffff90b166a40a00 -164582 Sometimes it is easier to see by finding a process getting starved and looking at the sched_info: crash> task ffff8eb765994500 sched_info PID: 7800 TASK: ffff8eb765994500 CPU: 16 COMMAND: "cputest" sched_info = { pcount = 8, run_delay = 697094208, last_arrival = 240260125039, last_queued = 240260327513 }, crash> task ffff8eb765994500 sched_info PID: 7800 TASK: ffff8eb765994500 CPU: 16 COMMAND: "cputest" sched_info = { pcount = 8, run_delay = 697094208, last_arrival = 240260125039, last_queued = 240260327513 }, Signed-off-by: Phil Auld Reviewed-by: Ben Segall Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: stable@vger.kernel.org Fixes: c06f04c70489 ("sched: Fix potential near-infinite distribute_cfs_runtime() loop") Link: http://lkml.kernel.org/r/20181008143639.GA4019@pauld.bos.csb Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

sched/fair: Fix vruntime_normalized() for remote non-migration wakeup

2018-09-29T10:06:07Z

commit d0cdb3ce8834332d918fc9c8ff74f8a169ec9abe upstream. When a task which previously ran on a given CPU is remotely queued to wake up on that same CPU, there is a period where the task's state is TASK_WAKING and its vruntime is not normalized. This is not accounted for in vruntime_normalized() which will cause an error in the task's vruntime if it is switched from the fair class during this time. For example if it is boosted to RT priority via rt_mutex_setprio(), rq->min_vruntime will not be subtracted from the task's vruntime but it will be added again when the task returns to the fair class. The task's vruntime will have been erroneously doubled and the effective priority of the task will be reduced. Note this will also lead to inflation of all vruntimes since the doubled vruntime value will become the rq's min_vruntime when other tasks leave the rq. This leads to repeated doubling of the vruntime and priority penalty. Fix this by recognizing a WAKING task's vruntime as normalized only if sched_remote_wakeup is true. This indicates a migration, in which case the vruntime would have been normalized in migrate_task_rq_fair(). Based on a similar patch from John Dias . Suggested-by: Peter Zijlstra Tested-by: Dietmar Eggemann Signed-off-by: Steve Muckle Signed-off-by: Peter Zijlstra (Intel) Cc: Chris Redpath Cc: John Dias Cc: Linus Torvalds Cc: Miguel de Dios Cc: Morten Rasmussen Cc: Patrick Bellasi Cc: Paul Turner Cc: Quentin Perret Cc: Thomas Gleixner Cc: Todd Kjos Cc: kernel-team@android.com Fixes: b5179ac70de8 ("sched/fair: Prepare to fix fairness problems on migration") Link: http://lkml.kernel.org/r/20180831224217.169476-1-smuckle@google.com Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

sched/fair: Fix util_avg of new tasks for asymmetric systems

2018-09-26T06:38:12Z

[ Upstream commit 8fe5c5a937d0f4e84221631833a2718afde52285 ] When a new task wakes-up for the first time, its initial utilization is set to half of the spare capacity of its CPU. The current implementation of post_init_entity_util_avg() uses SCHED_CAPACITY_SCALE directly as a capacity reference. As a result, on a big.LITTLE system, a new task waking up on an idle little CPU will be given ~512 of util_avg, even if the CPU's capacity is significantly less than that. Fix this by computing the spare capacity with arch_scale_cpu_capacity(). Signed-off-by: Quentin Perret Signed-off-by: Peter Zijlstra (Intel) Acked-by: Vincent Guittot Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dietmar.eggemann@arm.com Cc: morten.rasmussen@arm.com Cc: patrick.bellasi@arm.com Link: http://lkml.kernel.org/r/20180612112215.25448-1-quentin.perret@arm.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

sched/core: Use smp_mb() in wake_woken_function()

2018-09-26T06:38:10Z

[ Upstream commit 76e079fefc8f62bd9b2cd2950814d1ee806e31a5 ] wake_woken_function() synchronizes with wait_woken() as follows: [wait_woken] [wake_woken_function] entry->flags &= ~wq_flag_woken; condition = true; smp_mb(); smp_wmb(); if (condition) wq_entry->flags |= wq_flag_woken; break; This commit replaces the above smp_wmb() with an smp_mb() in order to guarantee that either wait_woken() sees the wait condition being true or the store to wq_entry->flags in woken_wake_function() follows the store in wait_woken() in the coherence order (so that the former can eventually be observed by wait_woken()). The commit also fixes a comment associated to set_current_state() in wait_woken(): the comment pairs the barrier in set_current_state() to the above smp_wmb(), while the actual pairing involves the barrier in set_current_state() and the barrier executed by the try_to_wake_up() in wake_woken_function(). Signed-off-by: Andrea Parri Signed-off-by: Paul E. McKenney Acked-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: akiyks@gmail.com Cc: boqun.feng@gmail.com Cc: dhowells@redhat.com Cc: j.alglave@ucl.ac.uk Cc: linux-arch@vger.kernel.org Cc: luc.maranget@inria.fr Cc: npiggin@gmail.com Cc: parri.andrea@gmail.com Cc: stern@rowland.harvard.edu Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/20180716180605.16115-10-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

sched/deadline: Fix switching to -deadline

2018-09-15T07:45:35Z

commit 295d6d5e373607729bcc8182c25afe964655714f upstream. Fix a bug introduced in: 72f9f3fdc928 ("sched/deadline: Remove dl_new from struct sched_dl_entity") After that commit, when switching to -deadline if the scheduling deadline of a task is in the past then switched_to_dl() calls setup_new_entity() to properly initialize the scheduling deadline and runtime. The problem is that the task is enqueued _before_ having its parameters initialized by setup_new_entity(), and this can cause problems. For example, a task with its out-of-date deadline in the past will potentially be enqueued as the highest priority one; however, its adjusted deadline may not be the earliest one. This patch fixes the problem by initializing the task's parameters before enqueuing it. Signed-off-by: luca abeni Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Daniel Bristot de Oliveira Cc: Juri Lelli Cc: Linus Torvalds Cc: Mathieu Poirier Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1504778971-13573-3-git-send-email-luca.abeni@santannapisa.it Signed-off-by: Ingo Molnar Signed-off-by: Sudip Mukherjee Signed-off-by: Greg Kroah-Hartman

sched/rt: Restore rt_runtime after disabling RT_RUNTIME_SHARE

2018-09-05T07:26:29Z

[ Upstream commit f3d133ee0a17d5694c6f21873eec9863e11fa423 ] NO_RT_RUNTIME_SHARE feature is used to prevent a CPU borrow enough runtime with a spin-rt-task. However, if RT_RUNTIME_SHARE feature is enabled and rt_rq has borrowd enough rt_runtime at the beginning, rt_runtime can't be restored to its initial bandwidth rt_runtime after we disable RT_RUNTIME_SHARE. E.g. on my PC with 4 cores, procedure to reproduce: 1) Make sure RT_RUNTIME_SHARE is enabled cat /sys/kernel/debug/sched_features GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU SIS_PROP NO_WARN_DOUBLE_CLOCK RT_PUSH_IPI RT_RUNTIME_SHARE NO_LB_MIN ATTACH_AGE_LOAD WA_IDLE WA_WEIGHT WA_BIAS 2) Start a spin-rt-task ./loop_rr & 3) set affinity to the last cpu taskset -p 8 $pid_of_loop_rr 4) Observe that last cpu have borrowed enough runtime. cat /proc/sched_debug | grep rt_runtime .rt_runtime : 950.000000 .rt_runtime : 900.000000 .rt_runtime : 950.000000 .rt_runtime : 1000.000000 5) Disable RT_RUNTIME_SHARE echo NO_RT_RUNTIME_SHARE > /sys/kernel/debug/sched_features 6) Observe that rt_runtime can not been restored cat /proc/sched_debug | grep rt_runtime .rt_runtime : 950.000000 .rt_runtime : 900.000000 .rt_runtime : 950.000000 .rt_runtime : 1000.000000 This patch help to restore rt_runtime after we disable RT_RUNTIME_SHARE. Signed-off-by: Hailong Liu Signed-off-by: Jiang Biao Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: zhong.weidong@zte.com.cn Link: http://lkml.kernel.org/r/1531874815-39357-1-git-send-email-liu.hailong6@zte.com.cn Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

sched/smt: Update sched_smt_present at runtime

2018-08-15T16:12:51Z

commit ba2591a5993eabcc8e874e30f361d8ffbb10d6d4 upstream The static key sched_smt_present is only updated at boot time when SMT siblings have been detected. Booting with maxcpus=1 and bringing the siblings online after boot rebuilds the scheduling domains correctly but does not update the static key, so the SMT code is not enabled. Let the key be updated in the scheduler CPU hotplug code to fix this. Signed-off-by: Peter Zijlstra Signed-off-by: Thomas Gleixner Reviewed-by: Konrad Rzeszutek Wilk Acked-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

sched/core: Require cpu_active() in select_task_rq(), for user tasks

2018-07-08T13:30:53Z

[ Upstream commit 7af443ee1697607541c6346c87385adab2214743 ] select_task_rq() is used in a few paths to select the CPU upon which a thread should be run - for example it is used by try_to_wake_up() & by fork or exec balancing. As-is it allows use of any online CPU that is present in the task's cpus_allowed mask. This presents a problem because there is a period whilst CPUs are brought online where a CPU is marked online, but is not yet fully initialized - ie. the period where CPUHP_AP_ONLINE_IDLE <= state < CPUHP_ONLINE. Usually we don't run any user tasks during this window, but there are corner cases where this can happen. An example observed is: - Some user task A, running on CPU X, forks to create task B. - sched_fork() calls __set_task_cpu() with cpu=X, setting task B's task_struct::cpu field to X. - CPU X is offlined. - Task A, currently somewhere between the __set_task_cpu() in copy_process() and the call to wake_up_new_task(), is migrated to CPU Y by migrate_tasks() when CPU X is offlined. - CPU X is onlined, but still in the CPUHP_AP_ONLINE_IDLE state. The scheduler is now active on CPU X, but there are no user tasks on the runqueue. - Task A runs on CPU Y & reaches wake_up_new_task(). This calls select_task_rq() with cpu=X, taken from task B's task_struct, and select_task_rq() allows CPU X to be returned. - Task A enqueues task B on CPU X's runqueue, via activate_task() & enqueue_task(). - CPU X now has a user task on its runqueue before it has reached the CPUHP_ONLINE state. In most cases, the user tasks that schedule on the newly onlined CPU have no idea that anything went wrong, but one case observed to be problematic is if the task goes on to invoke the sched_setaffinity syscall. The newly onlined CPU reaches the CPUHP_AP_ONLINE_IDLE state before the CPU that brought it online calls stop_machine_unpark(). This means that for a portion of the window of time between CPUHP_AP_ONLINE_IDLE & CPUHP_ONLINE the newly onlined CPU's struct cpu_stopper has its enabled field set to false. If a user thread is executed on the CPU during this window and it invokes sched_setaffinity with a CPU mask that does not include the CPU it's running on, then when __set_cpus_allowed_ptr() calls stop_one_cpu() intending to invoke migration_cpu_stop() and perform the actual migration away from the CPU it will simply return -ENOENT rather than calling migration_cpu_stop(). We then return from the sched_setaffinity syscall back to the user task that is now running on a CPU which it just asked not to run on, and which is not present in its cpus_allowed mask. This patch resolves the problem by having select_task_rq() enforce that user tasks run on CPUs that are active - the same requirement that select_fallback_rq() already enforces. This should ensure that newly onlined CPUs reach the CPUHP_AP_ACTIVE state before being able to schedule user tasks, and also implies that bringup_wait_for_ap() will have called stop_machine_unpark() which resolves the sched_setaffinity issue above. I haven't yet investigated them, but it may be of interest to review whether any of the actions performed by hotplug states between CPUHP_AP_ONLINE_IDLE & CPUHP_AP_ACTIVE could have similar unintended effects on user tasks that might schedule before they are reached, which might widen the scope of the problem from just affecting the behaviour of sched_setaffinity. Signed-off-by: Paul Burton Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20180526154648.11635-2-paul.burton@mips.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman