Re: [PATCH] [DISCUSS] Make the variable NULL after freeing it.

On Thu, 2006-12-28 at 09:54 +0100, Jan Engelhardt wrote:
On Dec 27 2006 17:10, Pavel Machek wrote:

Was just wondering if the _var_ in kfree(_var_) could be set to
NULL after its freed. It may solve the problem of accessing some
freed memory as the kernel will crash since _var_ was set to NULL.

Does this make sense? If yes, then how about renaming kfree to
something else and providing a kfree macro that would do the
following:

#define kfree(x) do { \
new_kfree(x); \
x = NULL; \
} while(0)

There might be other better ways too.

---- snip ----
(x) = NULL; \
---- snip ----
?

No, that would be very confusing. Otoh having
KFREE() do kfree() and assignment might be acceptable.

What about setting x to some poison value from <linux/poison.h>?

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).
Personally I think it is pointless to disallow "kfree(NULL)" by using
some poison value and force people to add a "we have to free that
variable" variable to work around it instead of keeping it NULL (which
makes the "kfree($variable)" a no-op).
Former discussions are to be found in the archives ......

Bernd
--
Firmix Software GmbH http://www.firmix.at/
mobil: +43 664 4416156 fax: +43 1 7890849-55
Embedded Linux Development and Services

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