On Sat, 20 Apr 2013 15:37:08 +0800 "zhangwei(Jovi)" <jovi.zhangwei@xxxxxxxxxx> wrote:
> Hi,
>
> Ingo, Steven, I get this patch from 3.4 preempt-rt patch set, It seems that this patch
> fix relayfs bug not only for rt kernel, but also for mainline.
>
> When I'm using below ktap script to tracing 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)
>
> I hope you can remember this :)
>
> so why we didn't commit this patch into mainline? any concern?
>
> Thanks.
>
> ------------------------------------->
> Subject: relay: fix timer madness
> From: Ingo Molnar <mingo@xxxxxxx>
>
> 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@xxxxxxx>
(This version of the patch should have your signed-off-by)
> @@ -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);
> }
We've "fixed" the printk-inside-runqueue-lock deadlocks via icky
hackery in wake_up_klogd(). I guess we could do it the same way here.
But the two approaches are conceptually very similar and this version
in relay.c is much simpler.
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