Messages in this thread | | | Subject | Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420 | From | Steven Rostedt <> | Date | Tue, 09 Mar 2010 12:28:23 -0500 |
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On Tue, 2010-03-09 at 11:35 +0800, Lai Jiangshan wrote: > Steven Rostedt wrote: > > On Mon, 2010-03-08 at 10:03 -0500, Steven Rostedt wrote: > > > >>> ringbuffer resizing and reseting will increase the ->record_disabled > >>> and then wait until a rcu_shced grace period passes. > >>> > >>> Contrarily, testing ->record_disabled should be at the same > >>> preempt disabled critical region as writing into ringbuffer, otherwise > >>> it will leave a window break ringbuffer resizing or reseting. > >> So the resizing and the resetting need a synchronize_sched() after the > >> disabling of the buffers, right? > > > > Looking at the code, the synchronize_sched() is already done in > > ring_buffer_resize, and the caller (trace.c:tracing_reset() ) also > > disables the ring buffer and calls synchronize_sched(). > > > > With that, what other window is still opened (after this fix)? > > > > This window is still opened: (RCU vs IDLE vs Tracing) > > synchronize_sched() does not protect preempt_disable()/enable() for > idle process. But tracing(function_graph, function) introduce more > preempt_disable()/enable() for idle process. It brings windows. > > I bet that this bug is not come from this window. > (I added some strict code to RCU and did stress test, > bug was still occurred.)
With Li's test, I was able to trigger the ring_buffer warning about resetting while committing. I was still able to trigger it with your patch to move the ring buffer disable code. But I did not trigger it with both the ring buffer disable code _and_ your RCU fix.
But I was able to trigger the segfault that Li is seeing. That is most likely a separate issue. I'm currently writing special debug code to find out why that is happening.
Thanks!
-- Steve
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