Re: 9pfs double kfree

[Al Viro <viro@ftp.linux.org.uk>]

On Mon, Mar 06, 2006 at 10:40:03AM +0200, Kai Makisara wrote:
> > Legal, but rather bad taste.  Init to NULL, possibly assign the value
> > if kmalloc(), then kfree() unconditionally - sure, but that... almost
> > certainly one hell of a lousy cleanup logics somewhere.
> > 
> I agree with you.
> 
> However, a few months ago it was advocated to let kfree take care of 
> testing the pointer against NULL and a load of patches like this:

That's different - that's _exactly_ the case I've mentioned above.

Moreover, that's exact match to standard behaviour of free(3):

C99 7.20.3.2(2):
The free function causes the space pointed to by ptr to be deallocated, that
is, made available for further allocation.  If ptr is a null pointer, no action
occurs.  Otherwise, if the argument does not match a pointer returned by the
calloc, malloc, or realloc function, or if the space has been deallocated by
a call to free or realloc, the behaviour is undefined.

IOW, free(NULL) is guaranteed to be no-op while double-free is nasal daemon
country.