Re: [PATCH] tracing/lockdep: turn lock->name into an array

[Ingo Molnar <mingo@elte.hu>]

* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> Hi
> 
> > Impact: allow filtering by lock name / fix module tracing
> > 
> > Currently, the "lock acquired" event is traced using a TRACE_EVENT.
> > But we can't use the char * type for the name without risking to
> > dereference a freed pointer. A lock name can come from a module
> > towards lockdep and it is risky to only store its address because we
> > defer its name printing.
> 
> When released lockdep string table? I guess it only happend at 
> module unloading. if so, we should consider to make delayed string 
> table freeing at module unloading.
> 
> My point is, module unloading is rare event. thus meking pointer 
> safe mechanism widely avoid string copy.
> 
> IOW, if not, ringbuffer is filled tons string. it kill the merit 
> of binary buffer and current design.

We could zap all pending trace entries on module unload (it is a 
rare operation). That would indeed make a whole category of 
symbol-alike string pointers safe to be passed by value.

	Ingo