Messages in this thread | | | Date | Fri, 1 Jun 2007 16:00:30 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777 warning |
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On Fri, 1 Jun 2007, Christoph Lameter wrote: > > Right it could catch a lot of other bugs as well.
I'd actually prefer "malloc(0)" to _not_ return NULL, but some known (non-NULL) bogus pointer.
Why?
Because it's quite sane to have simple logic like
ptr = malloc(size); if (!ptr) return -ENOMEM;
and writing it as
if (size && !ptr) return -ENOMEM;
is just annoying.
Also, NULL is _special_. There are absolutely tons of code in the kernel (and elsewhere) that just does something *different* from NULL pointers, and that totally breaks the whole notion of "you can allocate a zero-sized allocation, you just must not dereference it". If people special-case NULL as something else, they won't even go through the normal code-path.
So for *both* of the above reasons, it's actually stupid to return NULL for a zero-sized allocation. It would be much better to return another pointer that will trap on access. A good candidate might be to return
#define BADPTR ((void *)16)
which is a portable-enough (where "portable-enough" is "against strict ANSI C rules, but works in practice on all architectures") way to return something that will cause the same page fault behaviour as NULL, but will _not_ trigger the "NULL is special" code.
(Of course, you then need to teach "kfree()" to accept it as another pointer to be ignored, that's fine).
I bet you'd find *more* problems that way than by returning NULL, and you'd also avoid the whole problem with "if (!ptr) return -ENOMEM".
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