Messages in this thread |  | | | Subject | Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection | | From | Peter Zijlstra <> | | Date | Thu, 16 Apr 2009 19:20:07 +0200 |
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On Thu, 2009-04-16 at 13:03 -0400, Steven Rostedt wrote: > On Thu, 16 Apr 2009, Peter Zijlstra wrote: > > > On Thu, 2009-04-16 at 12:15 -0400, Steven Rostedt wrote: > > > plain text document attachment > > > (0002-tracing-events-lockdep-move-tracepoints-within-recu.patch) > > > From: Steven Rostedt <srostedt@redhat.com> > > > > > > With the current location of the tracepoints in lockdep, the system > > > can hard lockup in minutes when the tracepoints are enabled. > > > > > > Moving the tracepoints outside inside the lockdep protection solves > > > the issue. > > > > NAK > > > > the idea is to eventually move lockdep on top of the tracepoints. The > > tracer should grow to be more robust and handle recursion itself. > > > > Its likely a case of the tracer using a spinlock or mutex in the > > tracepoint code. When I did the tracepoints I converted one such to a > > raw_spinlock_t in the trace_print code. > > Note, that the ring buffer and events are made to be recursive. That is, > it allows one event to trace within another event.
But surely not in the same context. You could do a 4 level recursion protection like I did in perf-counter, not allowing recursion in:
nmi, irq, softirq, process - context.
That allows you to trace an irq while you're tracing something in process context, etc.. But not allow recursion on the same level.
> If the tracepoint is > triggered by something within the trace point handler, then we are > screwed. That needs to be fixed.
Exactly the thing you want to detect and warn about, preferably with a nice stack trace.
> I have not seen what is triggering back into locking. The ring buffer and > what I can see by the event code, does not grab any locks besides raw > ones.
Well, it used to all work, so something snuck in.
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