1. 15 Jul, 2018 1 commit
    • Isaac J. Manjarres's avatar
      stop_machine: Disable preemption when waking two stopper threads · 9fb8d5dc
      Isaac J. Manjarres authored
      When cpu_stop_queue_two_works() begins to wake the stopper threads, it does
      so without preemption disabled, which leads to the following race
      condition:
      
      The source CPU calls cpu_stop_queue_two_works(), with cpu1 as the source
      CPU, and cpu2 as the destination CPU. When adding the stopper threads to
      the wake queue used in this function, the source CPU stopper thread is
      added first, and the destination CPU stopper thread is added last.
      
      When wake_up_q() is invoked to wake the stopper threads, the threads are
      woken up in the order that they are queued in, so the source CPU's stopper
      thread is woken up first, and it preempts the thread running on the source
      CPU.
      
      The stopper thread will then execute on the source CPU, disable preemption,
      and begin executing multi_cpu_stop(), and wait for an ack from the
      destination CPU's stopper thread, with preemption still disabled. Since the
      worker thread that woke up the stopper thread on the source CPU is affine
      to the source CPU, and preemption is disabled on the source CPU, that
      thread will never run to dequeue the destination CPU's stopper thread from
      the wake queue, and thus, the destination CPU's stopper thread will never
      run, causing the source CPU's stopper thread to wait forever, and stall.
      
      Disable preemption when waking the stopper threads in
      cpu_stop_queue_two_works().
      
      Fixes: 0b26351b ("stop_machine, sched: Fix migrate_swap() vs. active_balance() deadlock")
      Co-Developed-by: default avatarPrasad Sodagudi <psodagud@codeaurora.org>
      Signed-off-by: default avatarPrasad Sodagudi <psodagud@codeaurora.org>
      Co-Developed-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
      Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
      Signed-off-by: default avatarIsaac J. Manjarres <isaacm@codeaurora.org>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: peterz@infradead.org
      Cc: matt@codeblueprint.co.uk
      Cc: bigeasy@linutronix.de
      Cc: gregkh@linuxfoundation.org
      Cc: stable@vger.kernel.org
      Link: https://lkml.kernel.org/r/1530655334-4601-1-git-send-email-isaacm@codeaurora.org
      9fb8d5dc
  2. 14 Jul, 2018 16 commits
  3. 13 Jul, 2018 15 commits
  4. 12 Jul, 2018 8 commits