From bd4596da4e1c726505f7b37aaded87a1ca64d727 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Fri, 19 Jul 2013 09:56:54 +1000 Subject: [PATCH] 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 Signed-off-by: "zhangwei(Jovi)" Cc: Steven Rostedt Cc: Jens Axboe Cc: Al Viro Cc: Eric Dumazet Signed-off-by: Andrew Morton --- kernel/relay.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/kernel/relay.c b/kernel/relay.c index 5001c9887db1..b91551397970 100644 --- 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; -- 2.39.2