linux-toradex.git/kernel/cpu.c, branch v4.9.62

smp/hotplug: Replace BUG_ON and react useful

2017-08-07T01:59:41+00:00

commit dea1d0f5f1284e3defee4b8484d9fc230686cd42 upstream.

The move of the unpark functions to the control thread moved the BUG_ON()
there as well. While it made some sense in the idle thread of the upcoming
CPU, it's bogus to crash the control thread on the already online CPU,
especially as the function has a return value and the callsite is prepared
to handle an error return.

Replace it with a WARN_ON_ONCE() and return a proper error code.

Fixes: 9cd4f1a4e7a8 ("smp/hotplug: Move unparking of percpu threads to the control CPU")
Rightfully-ranted-at-by: Linux Torvalds 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

smp/hotplug: Move unparking of percpu threads to the control CPU

2017-08-07T01:59:41+00:00

commit 9cd4f1a4e7a858849e889a081a99adff83e08e4c upstream.

Vikram reported the following backtrace:

   BUG: scheduling while atomic: swapper/7/0/0x00000002
   CPU: 7 PID: 0 Comm: swapper/7 Not tainted 4.9.32-perf+ #680
   schedule
   schedule_hrtimeout_range_clock
   schedule_hrtimeout
   wait_task_inactive
   __kthread_bind_mask
   __kthread_bind
   __kthread_unpark
   kthread_unpark
   cpuhp_online_idle
   cpu_startup_entry
   secondary_start_kernel

He analyzed correctly that a parked cpu hotplug thread of an offlined CPU
was still on the runqueue when the CPU came back online and tried to unpark
it. This causes the thread which invoked kthread_unpark() to call
wait_task_inactive() and subsequently schedule() with preemption disabled.
His proposed workaround was to "make sure" that a parked thread has
scheduled out when the CPU goes offline, so the situation cannot happen.

But that's still wrong because the root cause is not the fact that the
percpu thread is still on the runqueue and neither that preemption is
disabled, which could be simply solved by enabling preemption before
calling kthread_unpark().

The real issue is that the calling thread is the idle task of the upcoming
CPU, which is not supposed to call anything which might sleep.  The moron,
who wrote that code, missed completely that kthread_unpark() might end up
in schedule().

The solution is simpler than expected. The thread which controls the
hotplug operation is waiting for the CPU to call complete() on the hotplug
state completion. So the idle task of the upcoming CPU can set its state to
CPUHP_AP_ONLINE_IDLE and invoke complete(). This in turn wakes the control
task on a different CPU, which then can safely do the unpark and kick the
now unparked hotplug thread of the upcoming CPU to complete the bringup to
the final target state.

Control CPU                     AP

bringup_cpu();
  __cpu_up()  ------------>
				bringup_ap();
  bringup_wait_for_ap()
    wait_for_completion();
                                cpuhp_online_idle();
                <------------    complete();
    unpark(AP->stopper);
    unpark(AP->hotplugthread);
                                while(1)
                                  do_idle();
    kick(AP->hotplugthread);
    wait_for_completion();	hotplug_thread()
				  run_online_callbacks();
				  complete();

Fixes: 8df3e07e7f21 ("cpu/hotplug: Let upcoming cpu bring itself fully up")
Reported-by: Vikram Mulukutla 
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Cc: Sebastian Sewior 
Cc: Rusty Russell 
Cc: Tejun Heo 
Cc: Andrew Morton 
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1707042218020.2131@nanos
Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Drop the device lock on error

2017-06-14T13:06:04+00:00

commit 40da1b11f01e43aad1aa6cea64681b6125e8a2a7 upstream.

If a custom CPU target is specified and that one is not available _or_
can't be interrupted then the code returns to userland without dropping a
lock as notices by lockdep:

|echo 133 > /sys/devices/system/cpu/cpu7/hotplug/target
| ================================================
| [ BUG: lock held when returning to user space! ]
| ------------------------------------------------
| bash/503 is leaving the kernel with locks still held!
| 1 lock held by bash/503:
|  #0:  (device_hotplug_lock){+.+...}, at: [] lock_device_hotplug_sysfs+0x10/0x40

So release the lock then.

Fixes: 757c989b9994 ("cpu/hotplug: Make target state writeable")
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20170602142714.3ogo25f2wbq6fjpj@linutronix.de
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Serialize callback invocations proper

2017-05-08T05:47:55+00:00

commit dc434e056fe1dada20df7ba07f32739d3a701adf upstream.

The setup/remove_state/instance() functions in the hotplug core code are
serialized against concurrent CPU hotplug, but unfortunately not serialized
against themself.

As a consequence a concurrent invocation of these function results in
corruption of the callback machinery because two instances try to invoke
callbacks on remote cpus at the same time. This results in missing callback
invocations and initiator threads waiting forever on the completion.

The obvious solution to replace get_cpu_online() with cpu_hotplug_begin()
is not possible because at least one callsite calls into these functions
from a get_online_cpu() locked region.

Extend the protection scope of the cpuhp_state_mutex from solely protecting
the state arrays to cover the callback invocation machinery as well.

Fixes: 5b7aa87e0482 ("cpu/hotplug: Implement setup/removal interface")
Reported-and-tested-by: Bart Van Assche 
Signed-off-by: Sebastian Andrzej Siewior 
Cc: hpa@zytor.com
Cc: mingo@kernel.org
Cc: akpm@linux-foundation.org
Cc: torvalds@linux-foundation.org
Link: http://lkml.kernel.org/r/20170314150645.g4tdyoszlcbajmna@linutronix.de
Signed-off-by: Thomas Gleixner 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Greg Kroah-Hartman

hotplug: Make register and unregister notifier API symmetric

2017-01-06T09:40:10+00:00

commit 777c6e0daebb3fcefbbd6f620410a946b07ef6d0 upstream.

Yu Zhao has noticed that __unregister_cpu_notifier only unregisters its
notifiers when HOTPLUG_CPU=y while the registration might succeed even
when HOTPLUG_CPU=n if MODULE is enabled. This means that e.g. zswap
might keep a stale notifier on the list on the manual clean up during
the pool tear down and thus corrupt the list. Resulting in the following

[  144.964346] BUG: unable to handle kernel paging request at ffff880658a2be78
[  144.971337] IP: [] raw_notifier_chain_register+0x1b/0x40

[  145.122628] Call Trace:
[  145.125086]  [] __register_cpu_notifier+0x18/0x20
[  145.131350]  [] zswap_pool_create+0x273/0x400
[  145.137268]  [] __zswap_param_set+0x1fc/0x300
[  145.143188]  [] ? trace_hardirqs_on+0xd/0x10
[  145.149018]  [] ? kernel_param_lock+0x28/0x30
[  145.154940]  [] ? __might_fault+0x4f/0xa0
[  145.160511]  [] zswap_compressor_param_set+0x17/0x20
[  145.167035]  [] param_attr_store+0x5c/0xb0
[  145.172694]  [] module_attr_store+0x1d/0x30
[  145.178443]  [] sysfs_kf_write+0x4f/0x70
[  145.183925]  [] kernfs_fop_write+0x149/0x180
[  145.189761]  [] __vfs_write+0x18/0x40
[  145.194982]  [] vfs_write+0xb2/0x1a0
[  145.200122]  [] SyS_write+0x52/0xa0
[  145.205177]  [] entry_SYSCALL_64_fastpath+0x12/0x17

This can be even triggered manually by changing
/sys/module/zswap/parameters/compressor multiple times.

Fix this issue by making unregister APIs symmetric to the register so
there are no surprises.

Fixes: 47e627bc8c9a ("[PATCH] hotplug: Allow modules to use the cpu hotplug notifiers even if !CONFIG_HOTPLUG_CPU")
Reported-and-tested-by: Yu Zhao 
Signed-off-by: Michal Hocko 
Cc: linux-mm@kvack.org
Cc: Andrew Morton 
Cc: Dan Streetman 
Link: http://lkml.kernel.org/r/20161207135438.4310-1-mhocko@kernel.org
Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Use distinct name for cpu_hotplug.dep_map

2016-10-16T09:09:32+00:00

Use distinctive name for cpu_hotplug.dep_map to avoid the actual
cpu_hotplug.lock appearing as cpu_hotplug.lock#2 in lockdep splats.

Signed-off-by: Joonas Lahtinen 
Reviewed-by: Chris Wilson 
Acked-by: Gautham R. Shenoy 
Cc: Andrew Morton 
Cc: Daniel Vetter 
Cc: Gautham R . Shenoy 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: intel-gfx@lists.freedesktop.org
Cc: trivial@kernel.org
Signed-off-by: Ingo Molnar

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

2016-10-04T02:43:08+00:00

Pull CPU hotplug updates from Thomas Gleixner:
 "Yet another batch of cpu hotplug core updates and conversions:

   - Provide core infrastructure for multi instance drivers so the
     drivers do not have to keep custom lists.

   - Convert custom lists to the new infrastructure. The block-mq custom
     list conversion comes through the block tree and makes the diffstat
     tip over to more lines removed than added.

   - Handle unbalanced hotplug enable/disable calls more gracefully.

   - Remove the obsolete CPU_STARTING/DYING notifier support.

   - Convert another batch of notifier users.

   The relayfs changes which conflicted with the conversion have been
   shipped to me by Andrew.

   The remaining lot is targeted for 4.10 so that we finally can remove
   the rest of the notifiers"

* 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (46 commits)
  cpufreq: Fix up conversion to hotplug state machine
  blk/mq: Reserve hotplug states for block multiqueue
  x86/apic/uv: Convert to hotplug state machine
  s390/mm/pfault: Convert to hotplug state machine
  mips/loongson/smp: Convert to hotplug state machine
  mips/octeon/smp: Convert to hotplug state machine
  fault-injection/cpu: Convert to hotplug state machine
  padata: Convert to hotplug state machine
  cpufreq: Convert to hotplug state machine
  ACPI/processor: Convert to hotplug state machine
  virtio scsi: Convert to hotplug state machine
  oprofile/timer: Convert to hotplug state machine
  block/softirq: Convert to hotplug state machine
  lib/irq_poll: Convert to hotplug state machine
  x86/microcode: Convert to hotplug state machine
  sh/SH-X3 SMP: Convert to hotplug state machine
  ia64/mca: Convert to hotplug state machine
  ARM/OMAP/wakeupgen: Convert to hotplug state machine
  ARM/shmobile: Convert to hotplug state machine
  arm64/FP/SIMD: Convert to hotplug state machine
  ...

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

2016-10-03T17:29:53+00:00

Pull RCU updates from Ingo Molnar:
 "The main changes in this cycle were:

   - Expedited grace-period changes, most notably avoiding having user
     threads drive expedited grace periods, using a workqueue instead.

   - Miscellaneous fixes, including a performance fix for lists that was
     sent with the lists modifications.

   - CPU hotplug updates, most notably providing exact CPU-online
     tracking for RCU. This will in turn allow removal of the checks
     supporting RCU's prior heuristic that was based on the assumption
     that CPUs would take no longer than one jiffy to come online.

   - Torture-test updates.

   - Documentation updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (22 commits)
  list: Expand list_first_entry_or_null()
  torture: TOROUT_STRING(): Insert a space between flag and message
  rcuperf: Consistently insert space between flag and message
  rcutorture: Print out barrier error as document says
  torture: Add task state to writer-task stall printk()s
  torture: Convert torture_shutdown() to hrtimer
  rcutorture: Convert to hotplug state machine
  cpu/hotplug: Get rid of CPU_STARTING reference
  rcu: Provide exact CPU-online tracking for RCU
  rcu: Avoid redundant quiescent-state chasing
  rcu: Don't use modular infrastructure in non-modular code
  sched: Make wake_up_nohz_cpu() handle CPUs going offline
  rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads
  rcu: Use RCU's online-CPU state for expedited IPI retry
  rcu: Exclude RCU-offline CPUs from expedited grace periods
  rcu: Make expedited RCU CPU stall warnings respond to controls
  rcu: Stop disabling expedited RCU CPU stall warnings
  rcu: Drive expedited grace periods from workqueue
  rcu: Consolidate expedited grace period machinery
  documentation: Record reason for rcu_head two-byte alignment
  ...

slab: Convert to hotplug state machine

2016-09-06T16:30:20+00:00

Install the callbacks via the state machine.

Signed-off-by: Richard Weinberger 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Sebastian Andrzej Siewior 
Reviewed-by: Sebastian Andrzej Siewior 
Cc: Peter Zijlstra 
Cc: Pekka Enberg 
Cc: linux-mm@kvack.org
Cc: rt@linutronix.de
Cc: David Rientjes 
Cc: Joonsoo Kim 
Cc: Andrew Morton 
Cc: Christoph Lameter 
Link: http://lkml.kernel.org/r/20160823125319.abeapfjapf2kfezp@linutronix.de
Signed-off-by: Thomas Gleixner

relayfs: Convert to hotplug state machine

2016-09-06T16:30:20+00:00

Install the callbacks via the state machine. They are installed at run time but
relay_prepare_cpu() does not need to be invoked by the boot CPU because
relay_open() was not yet invoked and there are no pools that need to be created.

Signed-off-by: Richard Weinberger 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Sebastian Andrzej Siewior 
Reviewed-by: Sebastian Andrzej Siewior 
Cc: Peter Zijlstra 
Cc: rt@linutronix.de
Cc: Andrew Morton 
Link: http://lkml.kernel.org/r/20160818125731.27256-3-bigeasy@linutronix.de
Signed-off-by: Thomas Gleixner