Message-Id: <200701092257.l09MvM82029636@turing-police.cc.vt.edu>
To: Amit Choudhary <amit2030@yahoo.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>, Hua Zhong <hzhong@gmail.com>,
       Christoph Hellwig <hch@infradead.org>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] include/linux/slab.h: new KFREE() macro.
In-Reply-To: Your message of "Tue, 09 Jan 2007 11:02:35 PST."
             <88063.16727.qm@web55602.mail.re4.yahoo.com>
From: Valdis.Kletnieks@vt.edu
References: <88063.16727.qm@web55602.mail.re4.yahoo.com>
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On Tue, 09 Jan 2007 11:02:35 PST, Amit Choudhary said:
> Correct. And doing kfree(x); x=NULL; is not hiding that. These issues can still be debugged by
> using the slab debugging options. One other benefit of doing this is that if someone tries to
> access the same memory again using the variable 'x', then he will get an immediate crash. And the
> problem can be solved immediately, without using the slab debugging options. I do not yet
> understand how doing this hides the bugs, obfuscates the code, etc. because I haven't seen an
> example yet, but only blanket statements.

char *broken() {
	char *x, *y;
	x = kmalloc(100);
	y = x;
	kfree(x);
	x = NULL;
	return y;
}

Setting x to NULL doesn't do anything to fix the *real* bug here, because
the problematic reference is held in y, not x.  So you never get a crash
because somebody dereferences x.


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