linux.git/kernel/rcu, branch v5.8-rc2

Merge tag 'tty-5.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

2020-06-07T16:52:36+00:00

Pull tty/serial driver updates from Greg KH:
 "Here is the tty and serial driver updates for 5.8-rc1

  Nothing huge at all, just a lot of little serial driver fixes, updates
  for new devices and features, and other small things. Full details are
  in the shortlog.

  All of these have been in linux-next with no issues for a while"

* tag 'tty-5.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (67 commits)
  tty: serial: qcom_geni_serial: Add 51.2MHz frequency support
  tty: serial: imx: clear Ageing Timer Interrupt in handler
  serial: 8250_fintek: Add F81966 Support
  sc16is7xx: Add flag to activate IrDA mode
  dt-bindings: sc16is7xx: Add flag to activate IrDA mode
  serial: 8250: Support rs485 bus termination GPIO
  serial: 8520_port: Fix function param documentation
  dt-bindings: serial: Add binding for rs485 bus termination GPIO
  vt: keyboard: avoid signed integer overflow in k_ascii
  serial: 8250: Enable 16550A variants by default on non-x86
  tty: hvc_console, fix crashes on parallel open/close
  serial: imx: Initialize lock for non-registered console
  sc16is7xx: Read the LSR register for basic device presence check
  sc16is7xx: Allow sharing the IRQ line
  sc16is7xx: Use threaded IRQ
  sc16is7xx: Always use falling edge IRQ
  tty: n_gsm: Fix bogus i++ in gsm_data_kick
  tty: n_gsm: Remove unnecessary test in gsm_print_packet()
  serial: stm32: add no_console_suspend support
  tty: serial: fsl_lpuart: Use __maybe_unused instead of #if CONFIG_PM_SLEEP
  ...

Merge branch 'WIP.core/rcu' into core/rcu, to pick up two x86/entry dependencies

2020-06-01T09:47:29+00:00

Signed-off-by: Ingo Molnar

rcu: Allow for smp_call_function() running callbacks from idle

2020-05-28T08:50:12+00:00

Current RCU hard relies on smp_call_function() callbacks running from
interrupt context. A pending optimization is going to break that, it
will allow idle CPUs to run the callbacks from the idle loop. This
avoids raising the IPI on the requesting CPU and avoids handling an
exception on the receiving CPU.

Change rcu_is_cpu_rrupt_from_idle() to also accept task context,
provided it is the idle task.

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Reviewed-by: Paul E. McKenney 
Reviewed-by: Joel Fernandes (Google) 
Link: https://lore.kernel.org/r/20200527171236.GC706495@hirez.programming.kicks-ass.net

rcu: Provide rcu_irq_exit_check_preempt()

2020-05-26T17:05:11+00:00

Provide a debug check which can be invoked from exception return to kernel
mode before an attempt is made to schedule. Warn if RCU is not ready for
this.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Ingo Molnar 
Cc: Paul E. McKenney 
Link: https://lore.kernel.org/r/20200521202117.089709607@linutronix.de

rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()

2020-05-26T17:04:18+00:00

There will likely be exception handlers that can sleep, which rules
out the usual approach of invoking rcu_nmi_enter() on entry and also
rcu_nmi_exit() on all exit paths.  However, the alternative approach of
just not calling anything can prevent RCU from coaxing quiescent states
from nohz_full CPUs that are looping in the kernel:  RCU must instead
IPI them explicitly.  It would be better to enable the scheduler tick
on such CPUs to interact with RCU in a lighter-weight manner, and this
enabling is one of the things that rcu_nmi_enter() currently does.

What is needed is something that helps RCU coax quiescent states while
not preventing subsequent sleeps.  This commit therefore splits out the
nohz_full scheduler-tick enabling from the rest of the rcu_nmi_enter()
logic into a new function named rcu_irq_enter_check_tick().

[ tglx: Renamed the function and made it a nop when context tracking is off ]
[ mingo: Fixed a CONFIG_NO_HZ_FULL assumption, harmonized and fixed all the
         comment blocks and cleaned up rcu_nmi_enter()/exit() definitions. ]

Suggested-by: Andy Lutomirski 
Signed-off-by: Paul E. McKenney 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20200521202116.996113173@linutronix.de

rcu: Provide __rcu_is_watching()

2020-05-19T13:51:21+00:00

Same as rcu_is_watching() but without the preempt_disable/enable() pair
inside the function. It is merked noinstr so it ends up in the
non-instrumentable text section.

This is useful for non-preemptible code especially in the low level entry
section. Using rcu_is_watching() there results in a call to the
preempt_schedule_notrace() thunk which triggers noinstr section warnings in
objtool.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Link: https://lkml.kernel.org/r/20200512213810.518709291@linutronix.de

rcu: Provide rcu_irq_exit_preempt()

2020-05-19T13:51:21+00:00

Interrupts and exceptions invoke rcu_irq_enter() on entry and need to
invoke rcu_irq_exit() before they either return to the interrupted code or
invoke the scheduler due to preemption.

The general assumption is that RCU idle code has to have preemption
disabled so that a return from interrupt cannot schedule. So the return
from interrupt code invokes rcu_irq_exit() and preempt_schedule_irq().

If there is any imbalance in the rcu_irq/nmi* invocations or RCU idle code
had preemption enabled then this goes unnoticed until the CPU goes idle or
some other RCU check is executed.

Provide rcu_irq_exit_preempt() which can be invoked from the
interrupt/exception return code in case that preemption is enabled. It
invokes rcu_irq_exit() and contains a few sanity checks in case that
CONFIG_PROVE_RCU is enabled to catch such issues directly.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Paul E. McKenney 
Reviewed-by: Alexandre Chartre 
Acked-by: Peter Zijlstra 
Link: https://lkml.kernel.org/r/20200505134904.364456424@linutronix.de

rcu: Make RCU IRQ enter/exit functions rely on in_nmi()

2020-05-19T13:51:21+00:00

The rcu_nmi_enter_common() and rcu_nmi_exit_common() functions take an
"irq" parameter that indicates whether these functions have been invoked from
an irq handler (irq==true) or an NMI handler (irq==false).

However, recent changes have applied notrace to a few critical functions
such that rcu_nmi_enter_common() and rcu_nmi_exit_common() many now rely on
in_nmi().  Note that in_nmi() works no differently than before, but rather
that tracing is now prohibited in code regions where in_nmi() would
incorrectly report NMI state.

Therefore remove the "irq" parameter and inline rcu_nmi_enter_common() and
rcu_nmi_exit_common() into rcu_nmi_enter() and rcu_nmi_exit(),
respectively.

Signed-off-by: Paul E. McKenney 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Alexandre Chartre 
Link: https://lkml.kernel.org/r/20200505134101.617130349@linutronix.de

rcu/tree: Mark the idle relevant functions noinstr

2020-05-19T13:51:20+00:00

These functions are invoked from context tracking and other places in the
low level entry code. Move them into the .noinstr.text section to exclude
them from instrumentation.

Mark the places which are safe to invoke traceable functions with
instrumentation_begin/end() so objtool won't complain.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Alexandre Chartre 
Acked-by: Peter Zijlstra 
Acked-by: Paul E. McKenney 
Link: https://lkml.kernel.org/r/20200505134100.575356107@linutronix.de

rcu: constify sysrq_key_op

2020-05-15T12:53:20+00:00

With earlier commits, the API no longer discards the const-ness of the
sysrq_key_op. As such we can add the notation.

Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: linux-kernel@vger.kernel.org
Cc: "Paul E. McKenney" 
Cc: Josh Triplett 
Cc: rcu@vger.kernel.org
Reviewed-by: Paul E. McKenney 
Signed-off-by: Emil Velikov 
Link: https://lore.kernel.org/r/20200513214351.2138580-11-emil.l.velikov@gmail.com
Signed-off-by: Greg Kroah-Hartman