Merge tag 'timers-core-2020-08-14' of git://git.kernel.org/pub/scm/linux/kernel/git...

Pull more timer updates from Thomas Gleixner:
 "A set of posix CPU timer changes which allows to defer the heavy work
  of posix CPU timers into task work context. The tick interrupt is
  reduced to a quick check which queues the work which is doing the
  heavy lifting before returning to user space or going back to guest
  mode. Moving this out is deferring the signal delivery slightly but
  posix CPU timers are inaccurate by nature as they depend on the tick
  so there is no real damage. The relevant test cases all passed.

  This lifts the last offender for RT out of the hard interrupt context
  tick handler, but it also has the general benefit that the actual
  heavy work is accounted to the task/process and not to the tick
  interrupt itself.

  Further optimizations are possible to break long sighand lock hold and
  interrupt disabled (on !RT kernels) times when a massive amount of
  posix CPU timers (which are unpriviledged) is armed for a
  task/process.

  This is currently only enabled for x86 because the architecture has to
  ensure that task work is handled in KVM before entering a guest, which
  was just established for x86 with the new common entry/exit code which
  got merged post 5.8 and is not the case for other KVM architectures"

* tag 'timers-core-2020-08-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86: Select POSIX_CPU_TIMERS_TASK_WORK
  posix-cpu-timers: Provide mechanisms to defer timer handling to task_work
  posix-cpu-timers: Split run_posix_cpu_timers()

diff --combined arch/x86/Kconfig
index 9a28495,a82e715..7101ac6
--- 1/arch/x86/Kconfig
--- 2/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@@ -209,6 -209,7 +209,7 @@@ config X8
        select HAVE_PERF_REGS
        select HAVE_PERF_USER_STACK_DUMP
        select MMU_GATHER_RCU_TABLE_FREE                if PARAVIRT
+       select HAVE_POSIX_CPU_TIMERS_TASK_WORK
        select HAVE_REGS_AND_STACK_ACCESS_API
        select HAVE_RELIABLE_STACKTRACE         if X86_64 && (UNWINDER_FRAME_POINTER || UNWINDER_ORC) && STACK_VALIDATION
        select HAVE_FUNCTION_ARG_ACCESS_API
@@@ -803,7 -804,6 +804,7 @@@ config KVM_GUES
        depends on PARAVIRT
        select PARAVIRT_CLOCK
        select ARCH_CPUIDLE_HALTPOLL
 +      select X86_HV_CALLBACK_VECTOR
        default y
        help
          This option enables various optimizations for running under the KVM

diff --combined include/linux/sched.h
index 53ddc02,e9942ce..93ecd93
--- 1/include/linux/sched.h
--- 2/include/linux/sched.h
+++ b/include/linux/sched.h
@@@ -32,7 -32,6 +32,7 @@@
  #include <linux/task_io_accounting.h>
  #include <linux/posix-timers.h>
  #include <linux/rseq.h>
 +#include <linux/seqlock.h>
  #include <linux/kcsan.h>
  
  /* task_struct member predeclarations (sorted alphabetically): */
@@@ -890,6 -889,10 +890,10 @@@ struct task_struct 
        /* Empty if CONFIG_POSIX_CPUTIMERS=n */
        struct posix_cputimers          posix_cputimers;
  
+ #ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
+       struct posix_cputimers_work     posix_cputimers_work;
+ #endif
+ 
        /* Process credentials: */
  
        /* Tracer's credentials at attach: */
@@@ -1050,7 -1053,7 +1054,7 @@@
        /* Protected by ->alloc_lock: */
        nodemask_t                      mems_allowed;
        /* Seqence number to catch updates: */
 -      seqcount_t                      mems_allowed_seq;
 +      seqcount_spinlock_t             mems_allowed_seq;
        int                             cpuset_mem_spread_rotor;
        int                             cpuset_slab_spread_rotor;
  #endif
@@@ -1649,9 -1652,6 +1653,9 @@@ extern int idle_cpu(int cpu)
  extern int available_idle_cpu(int cpu);
  extern int sched_setscheduler(struct task_struct *, int, const struct sched_param *);
  extern int sched_setscheduler_nocheck(struct task_struct *, int, const struct sched_param *);
 +extern void sched_set_fifo(struct task_struct *p);
 +extern void sched_set_fifo_low(struct task_struct *p);
 +extern void sched_set_normal(struct task_struct *p, int nice);
  extern int sched_setattr(struct task_struct *, const struct sched_attr *);
  extern int sched_setattr_nocheck(struct task_struct *, const struct sched_attr *);
  extern struct task_struct *idle_task(int cpu);