1. 15 Aug, 2018 1 commit
    • Linus Torvalds's avatar
      init: rename and re-order boot_cpu_state_init() · b7722f4a
      Linus Torvalds authored
      commit b5b1404d upstream.
      This is purely a preparatory patch for upcoming changes during the 4.19
      merge window.
      We have a function called "boot_cpu_state_init()" that isn't really
      about the bootup cpu state: that is done much earlier by the similarly
      named "boot_cpu_init()" (note lack of "state" in name).
      This function initializes some hotplug CPU state, and needs to run after
      the percpu data has been properly initialized.  It even has a comment to
      that effect.
      Except it _doesn't_ actually run after the percpu data has been properly
      initialized.  On x86 it happens to do that, but on at least arm and
      arm64, the percpu base pointers are initialized by the arch-specific
      'smp_prepare_boot_cpu()' hook, which ran _after_ boot_cpu_state_init().
      This had some unexpected results, and in particular we have a patch
      pending for the merge window that did the obvious cleanup of using
      'this_cpu_write()' in the cpu hotplug init code:
        -       per_cpu_ptr(&cpuhp_state, smp_processor_id())->state = CPUHP_ONLINE;
        +       this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
      which is obviously the right thing to do.  Except because of the
      ordering issue, it actually failed miserably and unexpectedly on arm64.
      So this just fixes the ordering, and changes the name of the function to
      be 'boot_cpu_hotplug_init()' to make it obvious that it's about cpu
      hotplug state, because the core CPU state was supposed to have already
      been done earlier.
      Marked for stable, since the (not yet merged) patch that will show this
      problem is marked for stable.
      Reported-by: default avatarVlastimil Babka <vbabka@suse.cz>
      Reported-by: default avatarMian Yousaf Kaukab <yousaf.kaukab@suse.com>
      Suggested-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
      Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: Will Deacon <will.deacon@arm.com>
      Cc: stable@kernel.org
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
  2. 02 Jan, 2018 1 commit
  3. 14 Dec, 2017 1 commit
  4. 21 Oct, 2017 1 commit
    • Thomas Gleixner's avatar
      cpu/hotplug: Reset node state after operation · 1f7c70d6
      Thomas Gleixner authored
      The recent rework of the cpu hotplug internals changed the usage of the per
      cpu state->node field, but missed to clean it up after usage.
      So subsequent hotplug operations use the stale pointer from a previous
      operation and hand it into the callback functions. The callbacks then
      dereference a pointer which either belongs to a different facility or
      points to freed and potentially reused memory. In either case data
      corruption and crashes are the obvious consequence.
      Reset the node and the last pointers in the per cpu state to NULL after the
      operation which set them has completed.
      Fixes: 96abb968 ("smp/hotplug: Allow external multi-instance rollback")
      Reported-by: default avatarTvrtko Ursulin <tursulin@ursulin.net>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
      Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
      Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
      Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1710211606130.3213@nanos
  5. 25 Sep, 2017 6 commits
    • Peter Zijlstra's avatar
      smp/hotplug: Hotplug state fail injection · 1db49484
      Peter Zijlstra authored
      Add a sysfs file to one-time fail a specific state. This can be used
      to test the state rollback code paths.
      Something like this (hotplug-up.sh):
        echo 0 > /debug/sched_debug
        echo 1 > /debug/tracing/events/cpuhp/enable
        ALL_STATES=`cat /sys/devices/system/cpu/hotplug/states | cut -d':' -f1`
        for state in $STATES
      	  echo 0 > /sys/devices/system/cpu/cpu1/online
      	  echo 0 > /debug/tracing/trace
      	  echo Fail state: $state
      	  echo $state > /sys/devices/system/cpu/cpu1/hotplug/fail
      	  cat /sys/devices/system/cpu/cpu1/hotplug/fail
      	  echo 1 > /sys/devices/system/cpu/cpu1/online
      	  cat /debug/tracing/trace > hotfail-${state}.trace
      	  sleep 1
      Can be used to test for all possible rollback (barring multi-instance)
      scenarios on CPU-up, CPU-down is a trivial modification of the above.
      Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: bigeasy@linutronix.de
      Cc: efault@gmx.de
      Cc: rostedt@goodmis.org
      Cc: max.byungchul.park@gmail.com
      Link: https://lkml.kernel.org/r/20170920170546.972581715@infradead.org
    • Peter Zijlstra's avatar
      smp/hotplug: Differentiate the AP completion between up and down · 5ebe7742
      Peter Zijlstra authored
      With lockdep-crossrelease we get deadlock reports that span cpu-up and
      cpu-down chains. Such deadlocks cannot possibly happen because cpu-up
      and cpu-down are globally serialized.
      Now that we have consistent AP state, we can trivially separate the
      AP completion between up and down using st->bringup.
      Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Acked-by: max.byungchul.park@gmail.com
      Cc: bigeasy@linutronix.de
      Cc: efault@gmx.de
      Cc: rostedt@goodmis.org
      Link: https://lkml.kernel.org/r/20170920170546.872472799@infradead.org
    • Peter Zijlstra's avatar
      smp/hotplug: Differentiate the AP-work lockdep class between up and down · 5f4b55e1
      Peter Zijlstra authored
      With lockdep-crossrelease we get deadlock reports that span cpu-up and
      cpu-down chains. Such deadlocks cannot possibly happen because cpu-up
      and cpu-down are globally serialized.
        CPU0                  CPU1                    CPU2
        cpuhp_up_callbacks:   takedown_cpu:           cpuhp_thread_fun:
      Now that we have consistent AP state, we can trivially separate the
      AP-work class between up and down using st->bringup.
      Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: max.byungchul.park@gmail.com
      Cc: bigeasy@linutronix.de
      Cc: efault@gmx.de
      Cc: rostedt@goodmis.org
      Link: https://lkml.kernel.org/r/20170920170546.922524234@infradead.org
    • Peter Zijlstra's avatar
      smp/hotplug: Callback vs state-machine consistency · 724a8688
      Peter Zijlstra authored
      While the generic callback functions have an 'int' return and thus
      appear to be allowed to return error, this is not true for all states.
      Specifically, what used to be STARTING/DYING are ran with IRQs
      disabled from critical parts of CPU bringup/teardown and are not
      allowed to fail. Add WARNs to enforce this rule.
      But since some callbacks are indeed allowed to fail, we have the
      situation where a state-machine rollback encounters a failure, in this
      case we're stuck, we can't go forward and we can't go back. Also add a
      WARN for that case.
      AFAICT this is a fundamental 'problem' with no real obvious solution.
      We want the 'prepare' callbacks to allow failure on either up or down.
      Typically on prepare-up this would be things like -ENOMEM from
      resource allocations, and the typical usage in prepare-down would be
      something like -EBUSY to avoid CPUs being taken away.
      Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: bigeasy@linutronix.de
      Cc: efault@gmx.de
      Cc: rostedt@goodmis.org
      Cc: max.byungchul.park@gmail.com
      Link: https://lkml.kernel.org/r/20170920170546.819539119@infradead.org
    • Peter Zijlstra's avatar
      smp/hotplug: Rewrite AP state machine core · 4dddfb5f
      Peter Zijlstra authored
      There is currently no explicit state change on rollback. That is,
      st->bringup, st->rollback and st->target are not consistent when doing
      the rollback.
      Rework the AP state handling to be more coherent. This does mean we
      have to do a second AP kick-and-wait for rollback, but since rollback
      is the slow path of a slowpath, this really should not matter.
      Take this opportunity to simplify the AP thread function to only run a
      single callback per invocation. This unifies the three single/up/down
      modes is supports. The looping it used to do for up/down are achieved
      by retaining should_run and relying on the main smpboot_thread_fn()
      (I have most of a patch that does the same for the BP state handling,
      but that's not critical and gets a little complicated because
      CPUHP_BRINGUP_CPU does the AP handoff from a callback, which gets
      recursive @st usage, I still have de-fugly that.)
      [ tglx: Move cpuhp_down_callbacks() et al. into the HOTPLUG_CPU section to
        	avoid gcc complaining about unused functions. Make the HOTPLUG_CPU
        	one piece instead of having two consecutive ifdef sections of the
        	same type. ]
      Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: bigeasy@linutronix.de
      Cc: efault@gmx.de
      Cc: rostedt@goodmis.org
      Cc: max.byungchul.park@gmail.com
      Link: https://lkml.kernel.org/r/20170920170546.769658088@infradead.org
    • Peter Zijlstra's avatar
      smp/hotplug: Allow external multi-instance rollback · 96abb968
      Peter Zijlstra authored
      Currently the rollback of multi-instance states is handled inside
      cpuhp_invoke_callback(). The problem is that when we want to allow an
      explicit state change for rollback, we need to return from the
      function without doing the rollback.
      Change cpuhp_invoke_callback() to optionally return the multi-instance
      state, such that rollback can be done from a subsequent call.
      Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: bigeasy@linutronix.de
      Cc: efault@gmx.de
      Cc: rostedt@goodmis.org
      Cc: max.byungchul.park@gmail.com
      Link: https://lkml.kernel.org/r/20170920170546.720361181@infradead.org
  6. 14 Sep, 2017 1 commit
    • Thomas Gleixner's avatar
      watchdog/hardlockup/perf: Prevent CPU hotplug deadlock · 941154bd
      Thomas Gleixner authored
      The following deadlock is possible in the watchdog hotplug code:
                    ->park() := watchdog_disable()
                              ->destroy() := hw_perf_event_destroy()
      when a per cpu watchdog perf event is destroyed which drops the last
      reference to the PMU hardware. The cleanup code there invokes
      get_online_cpus() which instantly deadlocks because the hotplug percpu
      rwsem is write locked.
      To solve this add a deferring mechanism:
      This is still properly serialized against concurrent hotplug via the
      cpu_add_remove_lock, which is held by the task which initiated the hotplug
      This is also used to handle event destruction when the watchdog threads are
      parked via other mechanisms than CPU hotplug.
      Analyzed-by: default avatarPeter Zijlstra <peterz@infradead.org>
      Reported-by: default avatarBorislav Petkov <bp@alien8.de>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Reviewed-by: default avatarDon Zickus <dzickus@redhat.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Chris Metcalf <cmetcalf@mellanox.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Nicholas Piggin <npiggin@gmail.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Sebastian Siewior <bigeasy@linutronix.de>
      Cc: Ulrich Obergfell <uobergfe@redhat.com>
      Link: http://lkml.kernel.org/r/20170912194146.884469246@linutronix.deSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
  7. 25 Jul, 2017 1 commit
    • Paul E. McKenney's avatar
      rcu: Migrate callbacks earlier in the CPU-offline timeline · a58163d8
      Paul E. McKenney authored
      RCU callbacks must be migrated away from an outgoing CPU, and this is
      done near the end of the CPU-hotplug operation, after the outgoing CPU is
      long gone.  Unfortunately, this means that other CPU-hotplug callbacks
      can execute while the outgoing CPU's callbacks are still immobilized
      on the long-gone CPU's callback lists.  If any of these CPU-hotplug
      callbacks must wait, either directly or indirectly, for the invocation
      of any of the immobilized RCU callbacks, the system will hang.
      This commit avoids such hangs by migrating the callbacks away from the
      outgoing CPU immediately upon its departure, shortly after the return
      from __cpu_die() in takedown_cpu().  Thus, RCU is able to advance these
      callbacks and invoke them, which allows all the after-the-fact CPU-hotplug
      callbacks to wait on these RCU callbacks without risk of a hang.
      While in the neighborhood, this commit also moves rcu_send_cbs_to_orphanage()
      and rcu_adopt_orphan_cbs() under a pre-existing #ifdef to avoid including
      dead code on the one hand and to avoid define-without-use warnings on the
      other hand.
      Reported-by: default avatarJeffrey Hugo <jhugo@codeaurora.org>
      Link: http://lkml.kernel.org/r/db9c91f6-1b17-6136-84f0-03c3c2581ab4@codeaurora.orgSigned-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
      Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
      Cc: Richard Weinberger <richard@nod.at>
  8. 20 Jul, 2017 1 commit
    • Ethan Barnes's avatar
      smp/hotplug: Handle removal correctly in cpuhp_store_callbacks() · 0c96b273
      Ethan Barnes authored
      If cpuhp_store_callbacks() is called for CPUHP_AP_ONLINE_DYN or
      CPUHP_BP_PREPARE_DYN, which are the indicators for dynamically allocated
      states, then cpuhp_store_callbacks() allocates a new dynamic state. The
      first allocation in each range returns CPUHP_AP_ONLINE_DYN or
      If cpuhp_remove_state() is invoked for one of these states, then there is
      no protection against the allocation mechanism. So the removal, which
      should clear the callbacks and the name, gets a new state assigned and
      clears that one.
      As a consequence the state which should be cleared stays initialized. A
      consecutive CPU hotplug operation dereferences the state callbacks and
      accesses either freed or reused memory, resulting in crashes.
      Add a protection against this by checking the name argument for NULL. If
      it's NULL it's a removal. If not, it's an allocation.
      [ tglx: Added a comment and massaged changelog ]
      Fixes: 5b7aa87e ("cpu/hotplug: Implement setup/removal interface")
      Signed-off-by: default avatarEthan Barnes <ethan.barnes@sandisk.com>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.or>
      Cc: "Srivatsa S. Bhat" <srivatsa@mit.edu>
      Cc: Sebastian Siewior <bigeasy@linutronix.d>
      Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
      Cc: stable@vger.kernel.org
      Link: http://lkml.kernel.org/r/DM2PR04MB398242FC7776D603D9F99C894A60@DM2PR04MB398.namprd04.prod.outlook.com
  9. 11 Jul, 2017 1 commit
  10. 06 Jul, 2017 1 commit
    • Thomas Gleixner's avatar
      smp/hotplug: Move unparking of percpu threads to the control CPU · 9cd4f1a4
      Thomas Gleixner authored
      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
      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
        __cpu_up()  ------------>
                      <------------    complete();
          wait_for_completion();	hotplug_thread()
      Fixes: 8df3e07e ("cpu/hotplug: Let upcoming cpu bring itself fully up")
      Reported-by: default avatarVikram Mulukutla <markivx@codeaurora.org>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
      Cc: Sebastian Sewior <bigeasy@linutronix.de>
      Cc: Rusty Russell <rusty@rustcorp.com.au>
      Cc: Tejun Heo <tj@kernel.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1707042218020.2131@nanosSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
  11. 30 Jun, 2017 1 commit
  12. 22 Jun, 2017 1 commit
    • Thomas Gleixner's avatar
      genirq/cpuhotplug: Handle managed IRQs on CPU hotplug · c5cb83bb
      Thomas Gleixner authored
      If a CPU goes offline, interrupts affine to the CPU are moved away. If the
      outgoing CPU is the last CPU in the affinity mask the migration code breaks
      the affinity and sets it it all online cpus.
      This is a problem for affinity managed interrupts as CPU hotplug is often
      used for power management purposes. If the affinity is broken, the
      interrupt is not longer affine to the CPUs to which it was allocated.
      The affinity spreading allows to lay out multi queue devices in a way that
      they are assigned to a single CPU or a group of CPUs. If the last CPU goes
      offline, then the queue is not longer used, so the interrupt can be
      shutdown gracefully and parked until one of the assigned CPUs comes online
      Add a graceful shutdown mechanism into the irq affinity breaking code path,
      mark the irq as MANAGED_SHUTDOWN and leave the affinity mask unmodified.
      In the online path, scan the active interrupts for managed interrupts and
      if the interrupt is functional and the newly online CPU is part of the
      affinity mask, restart the interrupt if it is marked MANAGED_SHUTDOWN or if
      the interrupts is started up, try to add the CPU back to the effective
      affinity mask.
      Originally-by: default avatarChristoph Hellwig <hch@lst.de>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: Jens Axboe <axboe@kernel.dk>
      Cc: Marc Zyngier <marc.zyngier@arm.com>
      Cc: Michael Ellerman <mpe@ellerman.id.au>
      Cc: Keith Busch <keith.busch@intel.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Link: http://lkml.kernel.org/r/20170619235447.273417334@linutronix.de
  13. 12 Jun, 2017 1 commit
    • Arnd Bergmann's avatar
      cpu/hotplug: Remove unused check_for_tasks() function · 57de7212
      Arnd Bergmann authored
      clang -Wunused-function found one remaining function that was
      apparently meant to be removed in a recent code cleanup:
      kernel/cpu.c:565:20: warning: unused function 'check_for_tasks' [-Wunused-function]
      Sebastian explained: The function became unused unintentionally, but there
      is already a failure check, when a task cannot be removed from the outgoing
      cpu in the scheduler code, so bringing it back is not really giving any
      extra value.
      Fixes: 530e9b76 ("cpu/hotplug: Remove obsolete cpu hotplug register/unregister functions")
      Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
      Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
      Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
      Link: http://lkml.kernel.org/r/20170608085544.2257132-1-arnd@arndb.deSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
  14. 03 Jun, 2017 1 commit
  15. 26 May, 2017 6 commits
  16. 26 Mar, 2017 1 commit
  17. 14 Mar, 2017 1 commit
  18. 02 Mar, 2017 3 commits
  19. 18 Jan, 2017 1 commit
  20. 16 Jan, 2017 1 commit
  21. 27 Dec, 2016 1 commit
  22. 25 Dec, 2016 2 commits
  23. 21 Dec, 2016 1 commit
  24. 15 Dec, 2016 1 commit
  25. 08 Dec, 2016 1 commit
    • Michal Hocko's avatar
      hotplug: Make register and unregister notifier API symmetric · 777c6e0d
      Michal Hocko authored
      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: [<ffffffffa290b00b>] raw_notifier_chain_register+0x1b/0x40
      [  145.122628] Call Trace:
      [  145.125086]  [<ffffffffa28e5cf8>] __register_cpu_notifier+0x18/0x20
      [  145.131350]  [<ffffffffa2a5dd73>] zswap_pool_create+0x273/0x400
      [  145.137268]  [<ffffffffa2a5e0fc>] __zswap_param_set+0x1fc/0x300
      [  145.143188]  [<ffffffffa2944c1d>] ? trace_hardirqs_on+0xd/0x10
      [  145.149018]  [<ffffffffa2908798>] ? kernel_param_lock+0x28/0x30
      [  145.154940]  [<ffffffffa2a3e8cf>] ? __might_fault+0x4f/0xa0
      [  145.160511]  [<ffffffffa2a5e237>] zswap_compressor_param_set+0x17/0x20
      [  145.167035]  [<ffffffffa2908d3c>] param_attr_store+0x5c/0xb0
      [  145.172694]  [<ffffffffa290848d>] module_attr_store+0x1d/0x30
      [  145.178443]  [<ffffffffa2b2b41f>] sysfs_kf_write+0x4f/0x70
      [  145.183925]  [<ffffffffa2b2a5b9>] kernfs_fop_write+0x149/0x180
      [  145.189761]  [<ffffffffa2a99248>] __vfs_write+0x18/0x40
      [  145.194982]  [<ffffffffa2a9a412>] vfs_write+0xb2/0x1a0
      [  145.200122]  [<ffffffffa2a9a732>] SyS_write+0x52/0xa0
      [  145.205177]  [<ffffffffa2ff4d97>] 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: 47e627bc ("[PATCH] hotplug: Allow modules to use the cpu hotplug notifiers even if !CONFIG_HOTPLUG_CPU")
      Reported-and-tested-by: default avatarYu Zhao <yuzhao@google.com>
      Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
      Cc: linux-mm@kvack.org
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Dan Streetman <ddstreet@ieee.org>
      Link: http://lkml.kernel.org/r/20161207135438.4310-1-mhocko@kernel.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
  26. 16 Oct, 2016 1 commit
  27. 06 Sep, 2016 1 commit