Messages in this thread | | | Date | Thu, 16 Apr 2009 13:38:05 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection |
| |
On Thu, 16 Apr 2009, Peter Zijlstra wrote:
> 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.
Why not allow a nested interrupt to trace?
I don't want to add this logic to the lower levels, where only a few users need the protection. The protecting should be at the user level.
> > 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.
Its hard when you want to allow nesting.
> > > 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.
Note, it seems only the lockdep has issues with nesting. Perhaps when I can publish the lockless ring buffer this will all go away?
-- Steve
| |