rt-patches/0292-kernel-stop_machine-partly-revert-stop_machine-Use-r.patch

   1 From 1250e418e935851b501b7bda93e05a837fdd8448 Mon Sep 17 00:00:00 2001
   2 From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
   3 Date: Wed, 10 Feb 2016 18:25:16 +0100
   4 Subject: [PATCH 292/366] kernel/stop_machine: partly revert "stop_machine: Use
   5  raw spinlocks"
   6
   7 With completion using swait and so rawlocks we don't need this anymore.
   8 Further, bisect thinks this patch is responsible for:
   9
  10 |BUG: unable to handle kernel NULL pointer dereference at           (null)
  11 |IP: [<ffffffff81082123>] sched_cpu_active+0x53/0x70
  12 |PGD 0
  13 |Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
  14 |Dumping ftrace buffer:
  15 |   (ftrace buffer empty)
  16 |Modules linked in:
  17 |CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.4.1+ #330
  18 |Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Debian-1.8.2-1 04/01/2014
  19 |task: ffff88013ae64b00 ti: ffff88013ae74000 task.ti: ffff88013ae74000
  20 |RIP: 0010:[<ffffffff81082123>]  [<ffffffff81082123>] sched_cpu_active+0x53/0x70
  21 |RSP: 0000:ffff88013ae77eb8  EFLAGS: 00010082
  22 |RAX: 0000000000000001 RBX: ffffffff81c2cf20 RCX: 0000001050fb52fb
  23 |RDX: 0000001050fb52fb RSI: 000000105117ca1e RDI: 00000000001c7723
  24 |RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
  25 |R10: 0000000000000000 R11: 0000000000000001 R12: 00000000ffffffff
  26 |R13: ffffffff81c2cee0 R14: 0000000000000000 R15: 0000000000000001
  27 |FS:  0000000000000000(0000) GS:ffff88013b200000(0000) knlGS:0000000000000000
  28 |CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
  29 |CR2: 0000000000000000 CR3: 0000000001c09000 CR4: 00000000000006e0
  30 |Stack:
  31 | ffffffff810c446d ffff88013ae77f00 ffffffff8107d8dd 000000000000000a
  32 | 0000000000000001 0000000000000000 0000000000000000 0000000000000000
  33 | 0000000000000000 ffff88013ae77f10 ffffffff8107d90e ffff88013ae77f20
  34 |Call Trace:
  35 | [<ffffffff810c446d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
  36 | [<ffffffff8107d8dd>] ? notifier_call_chain+0x5d/0x80
  37 | [<ffffffff8107d90e>] ? __raw_notifier_call_chain+0xe/0x10
  38 | [<ffffffff810598a3>] ? cpu_notify+0x23/0x40
  39 | [<ffffffff8105a7b8>] ? notify_cpu_starting+0x28/0x30
  40
  41 during hotplug. The rawlocks need to remain however.
  42
  43 Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
  44 ---
  45  kernel/stop_machine.c | 40 ++++++++--------------------------------
  46  1 file changed, 8 insertions(+), 32 deletions(-)
  47
  48 diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
  49 index 2c5acc8..f84d3b4 100644
  50 --- a/kernel/stop_machine.c
  51 +++ b/kernel/stop_machine.c
  52 @@ -30,7 +30,7 @@ struct cpu_stop_done {
  53         atomic_t                nr_todo;        /* nr left to execute */
  54         bool                    executed;       /* actually executed? */
  55         int                     ret;            /* collected return value */
  56 -       struct task_struct      *waiter;        /* woken when nr_todo reaches 0 */
  57 +       struct completion       completion;     /* fired if nr_todo reaches 0 */
  58  };
  59
  60  /* the actual stopper, one per every possible cpu, enabled on online cpus */
  61 @@ -59,7 +59,7 @@ static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
  62  {
  63         memset(done, 0, sizeof(*done));
  64         atomic_set(&done->nr_todo, nr_todo);
  65 -       done->waiter = current;
  66 +       init_completion(&done->completion);
  67  }
  68
  69  /* signal completion unless @done is NULL */
  70 @@ -68,10 +68,8 @@ static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
  71         if (done) {
  72                 if (executed)
  73                         done->executed = true;
  74 -               if (atomic_dec_and_test(&done->nr_todo)) {
  75 -                       wake_up_process(done->waiter);
  76 -                       done->waiter = NULL;
  77 -               }
  78 +               if (atomic_dec_and_test(&done->nr_todo))
  79 +                       complete(&done->completion);
  80         }
  81  }
  82
  83 @@ -96,22 +94,6 @@ static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
  84         raw_spin_unlock_irqrestore(&stopper->lock, flags);
  85  }
  86
  87 -static void wait_for_stop_done(struct cpu_stop_done *done)
  88 -{
  89 -       set_current_state(TASK_UNINTERRUPTIBLE);
  90 -       while (atomic_read(&done->nr_todo)) {
  91 -               schedule();
  92 -               set_current_state(TASK_UNINTERRUPTIBLE);
  93 -       }
  94 -       /*
  95 -        * We need to wait until cpu_stop_signal_done() has cleared
  96 -        * done->waiter.
  97 -        */
  98 -       while (done->waiter)
  99 -               cpu_relax();
 100 -       set_current_state(TASK_RUNNING);
 101 -}
 102 -
 103  /**
 104   * stop_one_cpu - stop a cpu
 105   * @cpu: cpu to stop
 106 @@ -143,7 +125,7 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
 107
 108         cpu_stop_init_done(&done, 1);
 109         cpu_stop_queue_work(cpu, &work);
 110 -       wait_for_stop_done(&done);
 111 +       wait_for_completion(&done.completion);
 112         return done.executed ? done.ret : -ENOENT;
 113  }
 114
 115 @@ -302,7 +284,7 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
 116
 117         preempt_enable_nort();
 118
 119 -       wait_for_stop_done(&done);
 120 +       wait_for_completion(&done.completion);
 121
 122         return done.executed ? done.ret : -ENOENT;
 123  }
 124 @@ -364,7 +346,7 @@ static int __stop_cpus(const struct cpumask *cpumask,
 125
 126         cpu_stop_init_done(&done, cpumask_weight(cpumask));
 127         queue_stop_cpus_work(cpumask, fn, arg, &done, false);
 128 -       wait_for_stop_done(&done);
 129 +       wait_for_completion(&done.completion);
 130         return done.executed ? done.ret : -ENOENT;
 131  }
 132
 133 @@ -495,13 +477,7 @@ repeat:
 134                           kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
 135                                           ksym_buf), arg);
 136
 137 -               /*
 138 -                * Make sure that the wakeup and setting done->waiter
 139 -                * to NULL is atomic.
 140 -                */
 141 -               local_irq_disable();
 142                 cpu_stop_signal_done(done, true);
 143 -               local_irq_enable();
 144                 goto repeat;
 145         }
 146  }
 147 @@ -663,7 +639,7 @@ int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
 148         ret = multi_cpu_stop(&msdata);
 149
 150         /* Busy wait for completion. */
 151 -       while (atomic_read(&done.nr_todo))
 152 +       while (!completion_done(&done.completion))
 153                 cpu_relax();
 154
 155         mutex_unlock(&stop_cpus_mutex);
 156 --
 157 1.9.1
 158