linux.git/kernel/sched, branch v5.4-rc2

Merge tag 'copy-struct-from-user-v5.4-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

2019-10-04T17:36:31+00:00

Pull copy_struct_from_user() helper from Christian Brauner:
 "This contains the copy_struct_from_user() helper which got split out
  from the openat2() patchset. It is a generic interface designed to
  copy a struct from userspace.

  The helper will be especially useful for structs versioned by size of
  which we have quite a few. This allows for backwards compatibility,
  i.e. an extended struct can be passed to an older kernel, or a legacy
  struct can be passed to a newer kernel. For the first case (extended
  struct, older kernel) the new fields in an extended struct can be set
  to zero and the struct safely passed to an older kernel.

  The most obvious benefit is that this helper lets us get rid of
  duplicate code present in at least sched_setattr(), perf_event_open(),
  and clone3(). More importantly it will also help to ensure that users
  implementing versioning-by-size end up with the same core semantics.

  This point is especially crucial since we have at least one case where
  versioning-by-size is used but with slighly different semantics:
  sched_setattr(), perf_event_open(), and clone3() all do do similar
  checks to copy_struct_from_user() while rt_sigprocmask(2) always
  rejects differently-sized struct arguments.

  With this pull request we also switch over sched_setattr(),
  perf_event_open(), and clone3() to use the new helper"

* tag 'copy-struct-from-user-v5.4-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  usercopy: Add parentheses around assignment in test_copy_struct_from_user
  perf_event_open: switch to copy_struct_from_user()
  sched_setattr: switch to copy_struct_from_user()
  clone3: switch to copy_struct_from_user()
  lib: introduce copy_struct_from_user() helper

membarrier: Fix RCU locking bug caused by faulty merge

2019-10-01T19:27:50+00:00

The following commit:

  227a4aadc75b ("sched/membarrier: Fix p->mm->membarrier_state racy load")

got fat fingered by me when merging it with other patches. It meant to move
the RCU section out of the for loop but ended up doing it partially, leaving
a superfluous rcu_read_lock() inside, causing havok.

Reported-by: Ingo Molnar 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Borislav Petkov 
Cc: Chris Metcalf 
Cc: Christoph Lameter 
Cc: Eric W. Biederman 
Cc: Kirill Tkhai 
Cc: Linus Torvalds 
Cc: Mathieu Desnoyers 
Cc: Mike Galbraith 
Cc: Oleg Nesterov 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Russell King - ARM Linux admin 
Cc: Thomas Gleixner 
Cc: linux-tip-commits@vger.kernel.org
Fixes: 227a4aadc75b ("sched/membarrier: Fix p->mm->membarrier_state racy load")
Link: https://lkml.kernel.org/r/20191001085033.GP4519@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar

sched_setattr: switch to copy_struct_from_user()

2019-10-01T13:45:17+00:00

Switch sched_setattr() syscall from it's own copying struct sched_attr
from userspace to the new dedicated copy_struct_from_user() helper.

The change is very straightforward, and helps unify the syscall
interface for struct-from-userspace syscalls. Ideally we could also
unify sched_getattr(2)-style syscalls as well, but unfortunately the
correct semantics for such syscalls are much less clear (see [1] for
more detail). In future we could come up with a more sane idea for how
the syscall interface should look.

[1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
     robustify sched_read_attr() ABI logic and code")

Signed-off-by: Aleksa Sarai 
Reviewed-by: Kees Cook 
Reviewed-by: Christian Brauner 
[christian.brauner@ubuntu.com: improve commit message]
Link: https://lore.kernel.org/r/20191001011055.19283-4-cyphar@cyphar.com
Signed-off-by: Christian Brauner

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

2019-09-28T19:39:07+00:00

Pull scheduler fixes from Ingo Molnar:

 - Apply a number of membarrier related fixes and cleanups, which fixes
   a use-after-free race in the membarrier code

 - Introduce proper RCU protection for tasks on the runqueue - to get
   rid of the subtle task_rcu_dereference() interface that was easy to
   get wrong

 - Misc fixes, but also an EAS speedup

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Avoid redundant EAS calculation
  sched/core: Remove double update_max_interval() call on CPU startup
  sched/core: Fix preempt_schedule() interrupt return comment
  sched/fair: Fix -Wunused-but-set-variable warnings
  sched/core: Fix migration to invalid CPU in __set_cpus_allowed_ptr()
  sched/membarrier: Return -ENOMEM to userspace on memory allocation failure
  sched/membarrier: Skip IPIs when mm->mm_users == 1
  selftests, sched/membarrier: Add multi-threaded test
  sched/membarrier: Fix p->mm->membarrier_state racy load
  sched/membarrier: Call sync_core only before usermode for same mm
  sched/membarrier: Remove redundant check
  sched/membarrier: Fix private expedited registration check
  tasks, sched/core: RCUify the assignment of rq->curr
  tasks, sched/core: With a grace period after finish_task_switch(), remove unnecessary code
  tasks, sched/core: Ensure tasks are available for a grace period after leaving the runqueue
  tasks: Add a count of task RCU users
  sched/core: Convert vcpu_is_preempted() from macro to an inline function
  sched/fair: Remove unused cfs_rq_clock_task() function

sched/fair: Avoid redundant EAS calculation

2019-09-25T15:42:32+00:00

The EAS wake-up path computes the system energy for several CPU
candidates: the CPU with maximum spare capacity in each performance
domain, and the prev_cpu. However, if prev_cpu also happens to be the
CPU with maximum spare capacity in its performance domain, the energy
calculation is still done twice, unnecessarily.

Add a condition to filter out this corner case before doing the energy
calculation.

Reported-by: Pavan Kondeti 
Signed-off-by: Quentin Perret 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: dietmar.eggemann@arm.com
Cc: juri.lelli@redhat.com
Cc: morten.rasmussen@arm.com
Cc: qais.yousef@arm.com
Cc: rjw@rjwysocki.net
Cc: tkjos@google.com
Cc: valentin.schneider@arm.com
Cc: vincent.guittot@linaro.org
Fixes: eb92692b2544 ("sched/fair: Speed-up energy-aware wake-ups")
Link: https://lkml.kernel.org/r/20190920094115.GA11503@qperret.net
Signed-off-by: Ingo Molnar

sched/core: Remove double update_max_interval() call on CPU startup

2019-09-25T15:42:32+00:00

update_max_interval() is called in both CPUHP_AP_SCHED_STARTING's startup
and teardown callbacks, but it turns out it's also called at the end of
the startup callback of CPUHP_AP_ACTIVE (which is further down the
startup sequence).

There's no point in repeating this interval update in the startup sequence
since the CPU will remain online until it goes down the teardown path.

Remove the redundant call in sched_cpu_activate() (CPUHP_AP_ACTIVE).

Signed-off-by: Valentin Schneider 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: dietmar.eggemann@arm.com
Cc: juri.lelli@redhat.com
Cc: vincent.guittot@linaro.org
Link: https://lkml.kernel.org/r/20190923093017.11755-1-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar

sched/core: Fix preempt_schedule() interrupt return comment

2019-09-25T15:42:32+00:00

preempt_schedule_irq() is the one that should be called on return from
interrupt, clean up the comment to avoid any ambiguity.

Signed-off-by: Valentin Schneider 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Thomas Gleixner 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-riscv@lists.infradead.org
Cc: uclinux-h8-devel@lists.sourceforge.jp
Link: https://lkml.kernel.org/r/20190923143620.29334-2-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar

sched/fair: Fix -Wunused-but-set-variable warnings

2019-09-25T15:42:31+00:00

Commit:

   de53fd7aedb1 ("sched/fair: Fix low cpu usage with high throttling by removing expiration of cpu-local slices")

introduced a few compilation warnings:

  kernel/sched/fair.c: In function '__refill_cfs_bandwidth_runtime':
  kernel/sched/fair.c:4365:6: warning: variable 'now' set but not used [-Wunused-but-set-variable]
  kernel/sched/fair.c: In function 'start_cfs_bandwidth':
  kernel/sched/fair.c:4992:6: warning: variable 'overrun' set but not used [-Wunused-but-set-variable]

Also, __refill_cfs_bandwidth_runtime() does no longer update the
expiration time, so fix the comments accordingly.

Signed-off-by: Qian Cai 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Ben Segall 
Reviewed-by: Dave Chiluk 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: pauld@redhat.com
Fixes: de53fd7aedb1 ("sched/fair: Fix low cpu usage with high throttling by removing expiration of cpu-local slices")
Link: https://lkml.kernel.org/r/1566326455-8038-1-git-send-email-cai@lca.pw
Signed-off-by: Ingo Molnar

sched/core: Fix migration to invalid CPU in __set_cpus_allowed_ptr()

2019-09-25T15:42:31+00:00

An oops can be triggered in the scheduler when running qemu on arm64:

 Unable to handle kernel paging request at virtual address ffff000008effe40
 Internal error: Oops: 96000007 [#1] SMP
 Process migration/0 (pid: 12, stack limit = 0x00000000084e3736)
 pstate: 20000085 (nzCv daIf -PAN -UAO)
 pc : __ll_sc___cmpxchg_case_acq_4+0x4/0x20
 lr : move_queued_task.isra.21+0x124/0x298
 ...
 Call trace:
  __ll_sc___cmpxchg_case_acq_4+0x4/0x20
  __migrate_task+0xc8/0xe0
  migration_cpu_stop+0x170/0x180
  cpu_stopper_thread+0xec/0x178
  smpboot_thread_fn+0x1ac/0x1e8
  kthread+0x134/0x138
  ret_from_fork+0x10/0x18

__set_cpus_allowed_ptr() will choose an active dest_cpu in affinity mask to
migrage the process if process is not currently running on any one of the
CPUs specified in affinity mask. __set_cpus_allowed_ptr() will choose an
invalid dest_cpu (dest_cpu >= nr_cpu_ids, 1024 in my virtual machine) if
CPUS in an affinity mask are deactived by cpu_down after cpumask_intersects
check. cpumask_test_cpu() of dest_cpu afterwards is overflown and may pass if
corresponding bit is coincidentally set. As a consequence, kernel will
access an invalid rq address associate with the invalid CPU in
migration_cpu_stop->__migrate_task->move_queued_task and the Oops occurs.

The reproduce the crash:

  1) A process repeatedly binds itself to cpu0 and cpu1 in turn by calling
  sched_setaffinity.

  2) A shell script repeatedly does "echo 0 > /sys/devices/system/cpu/cpu1/online"
  and "echo 1 > /sys/devices/system/cpu/cpu1/online" in turn.

  3) Oops appears if the invalid CPU is set in memory after tested cpumask.

Signed-off-by: KeMeng Shi 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Valentin Schneider 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/1568616808-16808-1-git-send-email-shikemeng@huawei.com
Signed-off-by: Ingo Molnar

sched/membarrier: Return -ENOMEM to userspace on memory allocation failure

2019-09-25T15:42:31+00:00

Remove the IPI fallback code from membarrier to deal with very
infrequent cpumask memory allocation failure. Use GFP_KERNEL rather
than GFP_NOWAIT, and relax the blocking guarantees for the expedited
membarrier system call commands, allowing it to block if waiting for
memory to be made available.

In addition, now -ENOMEM can be returned to user-space if the cpumask
memory allocation fails.

Signed-off-by: Mathieu Desnoyers 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Chris Metcalf 
Cc: Christoph Lameter 
Cc: Eric W. Biederman 
Cc: Kirill Tkhai 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Oleg Nesterov 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Russell King - ARM Linux admin 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20190919173705.2181-8-mathieu.desnoyers@efficios.com
Signed-off-by: Ingo Molnar