Messages in this thread | | | Date | Sun, 31 Dec 2006 22:37:22 -0800 (PST) | From | Amit Choudhary <> | Subject | Re: [PATCH] [DISCUSS] Make the variable NULL after freeing it. |
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--- Ingo Oeser <ioe-lkml@rameria.de> wrote:
> On Sunday, 31. December 2006 14:38, Bernd Petrovitsch wrote: > > That depends on the decision/definition if (so called) "double free" is > > an error or not (and "free(NULL)" must work in POSIX-compliant > > environments). > > A double free of non-NULL is certainly an error. > So the idea of setting it to NULL is ok, since then you can > kfree the variable over and over again without any harm. > > It is just complicated to do this side effect free. > > Maybe one should check for builtin-constant and take the address, > if this is not an builtin-constant. > > sth, like this > > #define kfree_nullify(x) do { \ > if (__builtin_constant_p(x)) { \ > kfree(x); \ > } else { \ > typeof(x) *__addr_x = &x; \ > kfree(*__addr_x); \ > *__addr_x = NULL; \ > } \ > } while (0) > > Regards > > Ingo Oeser >
This is a nice approach but what if someone does kfree_nullify(x+20).
I decided to keep it simple. If someone is calling kfree_nullify() with anything other than a simple variable, then they should call kfree(). But definitely an approach that takes care of all situations is the best but I cannot think of a macro that can handle all situations. The simple macro that I sent earlier will catch all the other usage at compile time. Please let me know if I have missed something.
-Amit
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