rt-patches/0076-relay-Fix-timer-madness.patch

   1 From 15bdf68bea3b376dc7700b6c4a468fff40405a6b Mon Sep 17 00:00:00 2001
   2 From: Ingo Molnar <mingo@elte.hu>
   3 Date: Fri, 3 Jul 2009 08:44:07 -0500
   4 Subject: [PATCH 076/366] relay: Fix timer madness
   5
   6 remove timer calls (!!!) from deep within the tracing infrastructure.
   7 This was totally bogus code that can cause lockups and worse.  Poll
   8 the buffer every 2 jiffies for now.
   9
  10 Signed-off-by: Ingo Molnar <mingo@elte.hu>
  11 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  12 ---
  13  kernel/relay.c | 14 +++++---------
  14  1 file changed, 5 insertions(+), 9 deletions(-)
  15
  16 diff --git a/kernel/relay.c b/kernel/relay.c
  17 index 0b4570c..60684be 100644
  18 --- a/kernel/relay.c
  19 +++ b/kernel/relay.c
  20 @@ -336,6 +336,10 @@ static void wakeup_readers(unsigned long data)
  21  {
  22         struct rchan_buf *buf = (struct rchan_buf *)data;
  23         wake_up_interruptible(&buf->read_wait);
  24 +       /*
  25 +        * Stupid polling for now:
  26 +        */
  27 +       mod_timer(&buf->timer, jiffies + 1);
  28  }
  29
  30  /**
  31 @@ -353,6 +357,7 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init)
  32                 init_waitqueue_head(&buf->read_wait);
  33                 kref_init(&buf->kref);
  34                 setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
  35 +               mod_timer(&buf->timer, jiffies + 1);
  36         } else
  37                 del_timer_sync(&buf->timer);
  38
  39 @@ -736,15 +741,6 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
  40                 else
  41                         buf->early_bytes += buf->chan->subbuf_size -
  42                                             buf->padding[old_subbuf];
  43 -               smp_mb();
  44 -               if (waitqueue_active(&buf->read_wait))
  45 -                       /*
  46 -                        * Calling wake_up_interruptible() from here
  47 -                        * will deadlock if we happen to be logging
  48 -                        * from the scheduler (trying to re-grab
  49 -                        * rq->lock), so defer it.
  50 -                        */
  51 -                       mod_timer(&buf->timer, jiffies + 1);
  52         }
  53
  54         old = buf->data;
  55 --
  56 1.9.1
  57