Re: [PATCH 2/5] mm: remove unlikly NULL from kfree

[Pekka Enberg <penberg@cs.helsinki.fi>]

Hi Thomas,

On Wed, Mar 25, 2009 at 7:19 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > > This makes sense, since we now encourage developers to just call kfree
> > > without checking for NULL.

On Wed, 25 Mar 2009, Pekka Enberg wrote: 
> > But those are _error handling paths_ (at least supposed to be). I
> > wonder which call-sites are responsible for this. Can frtrace help us
> > here?

On Wed, 2009-03-25 at 08:50 +0100, Thomas Gleixner wrote:
> Why is this an error handler. We replaced tons of 
> 
>     if (obj)
>        kfree(obj);
> 
> constructs all over the kernel with kfree(obj); and let kfree deal
> with the NULL pointer.

We encourage developers not to check for kfree() in the common
out-of-memory error handling paths. But what Steven's results suggest is
that the common case is something like this:

   void *p = NULL;

   if (/* unlikely condition */)
       p = kmalloc(...);

   kfree(p);

which, quite frankly, doesn't make much sense to me. That's why I would
really want to know which call-sites are causing this before applying
the patch.

			Pekka