I guess they might have to switch to such an asynchronous delivery
system if they want to do this properly. Simply put, your polling
solution is exactly what I do, but I check a flag set by the writer
instead of waking up the readers unconditionally.
Mathieu
Ingo's solution could call waitqueue_active() inside wakeup_readers() to
determine if there are waiters. Right?
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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