linux/kernel/sched, branch v5.3

sched/core: Fix uclamp ABI bug, clean up and robustify sched_read_attr() ABI logic and code

2019-09-04T17:51:30Z

Thadeu Lima de Souza Cascardo reported that 'chrt' broke on recent kernels: $ chrt -p $$ chrt: failed to get pid 26306's policy: Argument list too long and he has root-caused the bug to the following commit increasing sched_attr size and breaking sched_read_attr() into returning -EFBIG: a509a7cd7974 ("sched/uclamp: Extend sched_setattr() to support utilization clamping") The other, bigger bug is that the whole sched_getattr() and sched_read_attr() logic of checking non-zero bits in new ABI components is arguably broken, and pretty much any extension of the ABI will spuriously break the ABI. That's way too fragile. Instead implement the perf syscall's extensible ABI instead, which we already implement on the sched_setattr() side: - if user-attributes have the same size as kernel attributes then the logic is unchanged. - if user-attributes are larger than the kernel knows about then simply skip the extra bits, but set attr->size to the (smaller) kernel size so that tooling can (in principle) handle older kernel as well. - if user-attributes are smaller than the kernel knows about then just copy whatever user-space can accept. Also clean up the whole logic: - Simplify the code flow - there's no need for 'ret' for example. - Standardize on 'kattr/uattr' and 'ksize/usize' naming to make sure we always know which side we are dealing with. - Why is it called 'read' when what it does is to copy to user? This code is so far away from VFS read() semantics that the naming is actively confusing. Name it sched_attr_copy_to_user() instead, which mirrors other copy_to_user() functionality. - Move the attr->size assignment from the head of sched_getattr() to the sched_attr_copy_to_user() function. Nothing else within the kernel should care about the size of the structure. With these fixes the sched_getattr() syscall now nicely supports an extensible ABI in both a forward and backward compatible fashion, and will also fix the chrt bug. As an added bonus the bogus -EFBIG return is removed as well, which as Thadeu noted should have been -E2BIG to begin with. Reported-by: Thadeu Lima de Souza Cascardo Tested-by: Dietmar Eggemann Tested-by: Thadeu Lima de Souza Cascardo Acked-by: Thadeu Lima de Souza Cascardo Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Patrick Bellasi Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: a509a7cd7974 ("sched/uclamp: Extend sched_setattr() to support utilization clamping") Link: https://lkml.kernel.org/r/20190904075532.GA26751@gmail.com Signed-off-by: Ingo Molnar

sched/fair: Don't assign runtime for throttled cfs_rq

2019-09-03T06:55:07Z

do_sched_cfs_period_timer() will refill cfs_b runtime and call distribute_cfs_runtime to unthrottle cfs_rq, sometimes cfs_b->runtime will allocate all quota to one cfs_rq incorrectly, then other cfs_rqs attached to this cfs_b can't get runtime and will be throttled. We find that one throttled cfs_rq has non-negative cfs_rq->runtime_remaining and cause an unexpetced cast from s64 to u64 in snippet: distribute_cfs_runtime() { runtime = -cfs_rq->runtime_remaining + 1; } The runtime here will change to a large number and consume all cfs_b->runtime in this cfs_b period. According to Ben Segall, the throttled cfs_rq can have account_cfs_rq_runtime called on it because it is throttled before idle_balance, and the idle_balance calls update_rq_clock to add time that is accounted to the task. This commit prevents cfs_rq to be assgined new runtime if it has been throttled until that distribute_cfs_runtime is called. Signed-off-by: Liangyan Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Ben Segall Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: shanpeic@linux.alibaba.com Cc: stable@vger.kernel.org Cc: xlpang@linux.alibaba.com Fixes: d3d9dc330236 ("sched: Throttle entities exceeding their allowed bandwidth") Link: https://lkml.kernel.org/r/20190826121633.6538-1-liangyan.peng@linux.alibaba.com Signed-off-by: Ingo Molnar

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

2019-08-25T17:06:12Z

Pull scheduler fix from Thomas Gleixner: "Handle the worker management in situations where a task is scheduled out on a PI lock contention correctly and schedule a new worker if possible" * 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched/core: Schedule new worker even if PI-blocked

psi: get poll_work to run when calling poll syscall next time

2019-08-25T02:48:42Z

Only when calling the poll syscall the first time can user receive POLLPRI correctly. After that, user always fails to acquire the event signal. Reproduce case: 1. Get the monitor code in Documentation/accounting/psi.txt 2. Run it, and wait for the event triggered. 3. Kill and restart the process. The question is why we can end up with poll_scheduled = 1 but the work not running (which would reset it to 0). And the answer is because the scheduling side sees group->poll_kworker under RCU protection and then schedules it, but here we cancel the work and destroy the worker. The cancel needs to pair with resetting the poll_scheduled flag. Link: http://lkml.kernel.org/r/1566357985-97781-1-git-send-email-joseph.qi@linux.alibaba.com Signed-off-by: Jason Xing Signed-off-by: Joseph Qi Reviewed-by: Caspar Zhang Reviewed-by: Suren Baghdasaryan Acked-by: Johannes Weiner Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

sched/core: Schedule new worker even if PI-blocked

2019-08-19T08:57:26Z

If a task is PI-blocked (blocking on sleeping spinlock) then we don't want to schedule a new kworker if we schedule out due to lock contention because !RT does not do that as well. A spinning spinlock disables preemption and a worker does not schedule out on lock contention (but spin). On RT the RW-semaphore implementation uses an rtmutex so tsk_is_pi_blocked() will return true if a task blocks on it. In this case we will now start a new worker which may deadlock if one worker is waiting on progress from another worker. Since a RW-semaphore starts a new worker on !RT, we should do the same on RT. XFS is able to trigger this deadlock. Allow to schedule new worker if the current worker is PI-blocked. Signed-off-by: Sebastian Andrzej Siewior Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20190816160626.12742-1-bigeasy@linutronix.de Signed-off-by: Ingo Molnar

Merge branch 'pm-cpufreq'

2019-08-16T12:24:51Z

* pm-cpufreq: cpufreq: schedutil: Don't skip freq update when limits change cpufreq: dev_pm_qos_update_request() can return 1 on success

cpufreq: schedutil: Don't skip freq update when limits change

2019-08-10T11:53:19Z

To avoid reducing the frequency of a CPU prematurely, we skip reducing the frequency if the CPU had been busy recently. This should not be done when the limits of the policy are changed, for example due to thermal throttling. We should always get the frequency within the new limits as soon as possible. Trying to fix this by using only one flag, i.e. need_freq_update, can lead to a race condition where the flag gets cleared without forcing us to change the frequency at least once. And so this patch introduces another flag to avoid that race condition. Fixes: ecd288429126 ("cpufreq: schedutil: Don't set next_freq to UINT_MAX") Cc: v4.18+ # v4.18+ Reported-by: Doug Smythies Tested-by: Doug Smythies Signed-off-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki

sched/psi: Do not require setsched permission from the trigger creator

2019-08-06T10:49:18Z

When a process creates a new trigger by writing into /proc/pressure/* files, permissions to write such a file should be used to determine whether the process is allowed to do so or not. Current implementation would also require such a process to have setsched capability. Setting of psi trigger thread's scheduling policy is an implementation detail and should not be exposed to the user level. Remove the permission check by using _nocheck version of the function. Suggested-by: Nick Kralevich Signed-off-by: Suren Baghdasaryan Signed-off-by: Peter Zijlstra (Intel) Cc: lizefan@huawei.com Cc: mingo@redhat.com Cc: akpm@linux-foundation.org Cc: kernel-team@android.com Cc: dennisszhou@gmail.com Cc: dennis@kernel.org Cc: hannes@cmpxchg.org Cc: axboe@kernel.dk Link: https://lkml.kernel.org/r/20190730013310.162367-1-surenb@google.com

sched/psi: Reduce psimon FIFO priority

2019-08-06T10:49:18Z

PSI defaults to a FIFO-99 thread, reduce this to FIFO-1. FIFO-99 is the very highest priority available to SCHED_FIFO and it not a suitable default; it would indicate the psi work is the most important work on the machine. Since Real-Time tasks will have pre-allocated memory and locked it in place, Real-Time tasks do not care about PSI. All it needs is to be above OTHER. Signed-off-by: Peter Zijlstra (Intel) Acked-by: Johannes Weiner Tested-by: Suren Baghdasaryan Cc: Thomas Gleixner

sched/deadline: Fix double accounting of rq/running bw in push & pull

2019-08-06T10:49:18Z

{push,pull}_dl_task() always calls {de,}activate_task() with .flags=0 which sets p->on_rq=TASK_ON_RQ_MIGRATING. {push,pull}_dl_task()->{de,}activate_task()->{de,en}queue_task()-> {de,en}queue_task_dl() calls {sub,add}_{running,rq}_bw() since p->on_rq==TASK_ON_RQ_MIGRATING. So {sub,add}_{running,rq}_bw() in {push,pull}_dl_task() is double-accounting for that task. Fix it by removing rq/running bw accounting in [push/pull]_dl_task(). Fixes: 7dd778841164 ("sched/core: Unify p->on_rq updates") Signed-off-by: Dietmar Eggemann Signed-off-by: Peter Zijlstra (Intel) Cc: Valentin Schneider Cc: Ingo Molnar Cc: Luca Abeni Cc: Daniel Bristot de Oliveira Cc: Juri Lelli Cc: Qais Yousef Link: https://lkml.kernel.org/r/20190802145945.18702-2-dietmar.eggemann@arm.com