linux.git/arch/arm/kernel/smp.c, branch v5.14

sched/core: Initialize the idle task with preemption disabled

2021-05-12T11:01:45+00:00

As pointed out by commit

  de9b8f5dcbd9 ("sched: Fix crash trying to dequeue/enqueue the idle thread")

init_idle() can and will be invoked more than once on the same idle
task. At boot time, it is invoked for the boot CPU thread by
sched_init(). Then smp_init() creates the threads for all the secondary
CPUs and invokes init_idle() on them.

As the hotplug machinery brings the secondaries to life, it will issue
calls to idle_thread_get(), which itself invokes init_idle() yet again.
In this case it's invoked twice more per secondary: at _cpu_up(), and at
bringup_cpu().

Given smp_init() already initializes the idle tasks for all *possible*
CPUs, no further initialization should be required. Now, removing
init_idle() from idle_thread_get() exposes some interesting expectations
with regards to the idle task's preempt_count: the secondary startup always
issues a preempt_disable(), requiring some reset of the preempt count to 0
between hot-unplug and hotplug, which is currently served by
idle_thread_get() -> idle_init().

Given the idle task is supposed to have preemption disabled once and never
see it re-enabled, it seems that what we actually want is to initialize its
preempt_count to PREEMPT_DISABLED and leave it there. Do that, and remove
init_idle() from idle_thread_get().

Secondary startups were patched via coccinelle:

  @begone@
  @@

  -preempt_disable();
  ...
  cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);

Signed-off-by: Valentin Schneider 
Signed-off-by: Ingo Molnar 
Acked-by: Peter Zijlstra 
Link: https://lore.kernel.org/r/20210512094636.2958515-1-valentin.schneider@arm.com

ARM: 9047/1: smp: remove unused variable

2021-02-01T19:42:13+00:00

Not used anymore after refactoring:

arch/arm/kernel/smp.c: In function ‘show_ipi_list’:
arch/arm/kernel/smp.c:543:16: warning: variable ‘irq’ set but not used [-Wunused-but-set-variable]
  543 |   unsigned int irq;

Fixes: 88c637748e31 ("ARM: smp: Use irq_desc_kstat_cpu() in show_ipi_list()")
Signed-off-by: Wolfram Sang 
Cc: Thomas Gleixner 
Cc: Marc Zyngier 
Signed-off-by: Russell King

Merge tag 'irq-core-2020-12-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2020-12-24T21:50:23+00:00

Pull irq updates from Thomas Gleixner:
 "This is the second attempt after the first one failed miserably and
  got zapped to unblock the rest of the interrupt related patches.

  A treewide cleanup of interrupt descriptor (ab)use with all sorts of
  racy accesses, inefficient and disfunctional code. The goal is to
  remove the export of irq_to_desc() to prevent these things from
  creeping up again"

* tag 'irq-core-2020-12-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits)
  genirq: Restrict export of irq_to_desc()
  xen/events: Implement irq distribution
  xen/events: Reduce irq_info:: Spurious_cnt storage size
  xen/events: Only force affinity mask for percpu interrupts
  xen/events: Use immediate affinity setting
  xen/events: Remove disfunct affinity spreading
  xen/events: Remove unused bind_evtchn_to_irq_lateeoi()
  net/mlx5: Use effective interrupt affinity
  net/mlx5: Replace irq_to_desc() abuse
  net/mlx4: Use effective interrupt affinity
  net/mlx4: Replace irq_to_desc() abuse
  PCI: mobiveil: Use irq_data_get_irq_chip_data()
  PCI: xilinx-nwl: Use irq_data_get_irq_chip_data()
  NTB/msi: Use irq_has_action()
  mfd: ab8500-debugfs: Remove the racy fiddling with irq_desc
  pinctrl: nomadik: Use irq_has_action()
  drm/i915/pmu: Replace open coded kstat_irqs() copy
  drm/i915/lpe_audio: Remove pointless irq_to_desc() usage
  s390/irq: Use irq_desc_kstat_cpu() in show_msi_interrupt()
  parisc/irq: Use irq_desc_kstat_cpu() in show_interrupts()
  ...

ARM: 9033/1: arm/smp: Drop the macro S(x,s)

2020-12-21T11:19:19+00:00

Mapping between IPI type index and its string is direct without requiring
an additional offset. Hence the existing macro S(x, s) is now redundant
and can just be dropped. This also makes the code clean and simple.

Cc: Marc Zyngier 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual 
Signed-off-by: Russell King

ARM: smp: Use irq_desc_kstat_cpu() in show_ipi_list()

2020-12-15T15:19:31+00:00

The irq descriptor is already there, no need to look it up again.

Signed-off-by: Thomas Gleixner 
Acked-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20201210194043.454288890@linutronix.de

ARM: Handle no IPI being registered in show_ipi_list()

2020-09-28T10:32:04+00:00

As SMP-on-UP is a valid configuration on 32bit ARM, do not assume that
IPIs are populated in show_ipi_list().

Reported-by: Guillaume Tucker 
Reported-by: kernelci.org bot 
Tested-by: Guillaume Tucker 
Signed-off-by: Marc Zyngier

arm: Move ipi_teardown() to a CONFIG_HOTPLUG_CPU section

2020-09-18T16:40:48+00:00

ipi_teardown() is only used when CONFIG_HOTPLUG_CPU is enabled.
Move the function to a location guarded by this config option.

Signed-off-by: Marc Zyngier

ARM: Remove custom IRQ stat accounting

2020-09-17T15:37:28+00:00

Let's switch the arm code to the core accounting, which already
does everything we need.

Reviewed-by: Valentin Schneider 
Signed-off-by: Marc Zyngier

ARM: Kill __smp_cross_call and co

2020-09-17T15:37:28+00:00

The old IPI registration interface is now unused on arm, so let's
get rid of it.

Reviewed-by: Valentin Schneider 
Signed-off-by: Marc Zyngier

ARM: Allow IPIs to be handled as normal interrupts

2020-09-13T16:05:39+00:00

In order to deal with IPIs as normal interrupts, let's add
a new way to register them with the architecture code.

set_smp_ipi_range() takes a range of interrupts, and allows
the arch code to request them as if the were normal interrupts.
A standard handler is then called by the core IRQ code to deal
with the IPI.

This means that we don't need to call irq_enter/irq_exit, and
that we don't need to deal with set_irq_regs either. So let's
move the dispatcher into its own function, and leave handle_IPI()
as a compatibility function.

On the sending side, let's make use of ipi_send_mask, which
already exists for this purpose.

One of the major difference is that we end up, in some cases
(such as when performing IRQ time accounting on the scheduler
IPI), end up with nested irq_enter()/irq_exit() pairs.
Other than the (relatively small) overhead, there should be
no consequences to it (these pairs are designed to nest
correctly, and the accounting shouldn't be off).

Reviewed-by: Valentin Schneider 
Signed-off-by: Marc Zyngier