* Ankita Garg <[email protected]> wrote:
> local_irq_save(flags);
> buf = _stp_chan->buf[smp_processor_id()];
> if (unlikely(buf->offset + length > _stp_chan->subbuf_size))
> length = relay_switch_subbuf(buf, length);
> memcpy(buf->data + buf->offset, data, length);
> buf->offset += length;
> local_irq_restore(flags);
oh, what a fine piece of s^H^H :-/ Who in their right mind calls this
from _tracing_ code:
smp_mb();
if (waitqueue_active(&buf->read_wait))
/*
* Calling wake_up_interruptible() from here
* will deadlock if we happen to be logging
* from the scheduler (trying to re-grab
* rq->lock), so defer it.
*/
__mod_timer(&buf->timer, jiffies + 1);
and the comment is utter rubbish: __mod_timer() can lock up just as
much. Just use an adaptive-polling method to drive the draining of the
relay buffer, instead of mucking with timers from within the tracing
code. Whoever implemented this has absolutely zero clue i have to say
...
the smp_mb() is rubbish too.
could you try the patch below, does it fix the problem?
Ingo
------------------------------------->
Subject: relay: fix timer madness
From: Ingo Molnar <[email protected]>
remove timer calls (!!!) from deep within the tracing infrastructure.
This was totally bogus code that can cause lockups and worse.
Poll the buffer every 2 jiffies for now.
Signed-off-by: Ingo Molnar <[email protected]>
---
kernel/relay.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
Index: linux-rt-rebase.q/kernel/relay.c
===================================================================
--- linux-rt-rebase.q.orig/kernel/relay.c
+++ linux-rt-rebase.q/kernel/relay.c
@@ -319,6 +319,10 @@ static void wakeup_readers(unsigned long
{
struct rchan_buf *buf = (struct rchan_buf *)data;
wake_up_interruptible(&buf->read_wait);
+ /*
+ * Stupid polling for now:
+ */
+ mod_timer(&buf->timer, jiffies + 1);
}
/**
@@ -336,6 +340,7 @@ static void __relay_reset(struct rchan_b
init_waitqueue_head(&buf->read_wait);
kref_init(&buf->kref);
setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
+ mod_timer(&buf->timer, jiffies + 1);
} else
del_timer_sync(&buf->timer);
@@ -604,15 +609,6 @@ size_t relay_switch_subbuf(struct rchan_
buf->subbufs_produced++;
buf->dentry->d_inode->i_size += buf->chan->subbuf_size -
buf->padding[old_subbuf];
- smp_mb();
- if (waitqueue_active(&buf->read_wait))
- /*
- * Calling wake_up_interruptible() from here
- * will deadlock if we happen to be logging
- * from the scheduler (trying to re-grab
- * rq->lock), so defer it.
- */
- __mod_timer(&buf->timer, jiffies + 1);
}
old = buf->data;
-
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