relay: fix timer madness

When I'm using below ktap script to trace all event tracepoints, without
this patch, the system will hang in few seconds, the patch indeed fix the
problem as the changelog pointed.

	function eventfun (e) {
        	printf("%d %d\t%s\t%s", cpu(), pid(), execname(), e.annotate)
	}

	kdebug.probe("tp:", eventfun)

	kdebug.probe_end(function () {
        	printf("probe end\n")
	})

This patch is old, I can found the original patch discussion in 2007.
http://marc.info/?l=linux-kernel&m=118544794717162&w=2 (In that mail
thread, the patch didn't fix that problem, but it fix the problem I
encountered now)

Ingo's original changelog:

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 <mingo@elte.hu>
Signed-off-by: "zhangwei(Jovi)" <jovi.zhangwei@huawei.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/relay.c b/kernel/relay.c
index 5001c9887db1a3ea22cb03d5dd843b1a44a2e1c5..b91551397970546ac0bdf69c4937ce76118aebaa 100644 (file)
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -339,6 +339,10 @@ static void wakeup_readers(unsigned long data)
 {
        struct rchan_buf *buf = (struct rchan_buf *)data;
        wake_up_interruptible(&buf->read_wait);
+       /*
+        * Stupid polling for now:
+        */
+       mod_timer(&buf->timer, jiffies + 1);
 }
 
 /**
@@ -356,6 +360,7 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init)
                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);
 
@@ -739,15 +744,6 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
                else
                        buf->early_bytes += 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;