Re: Is it OK to pass non-acquired objects to kfree?

[Dmitry Vyukov <dvyukov@google.com>]

On Thu, Sep 10, 2015 at 8:13 PM, Christoph Lameter <cl@linux.com> wrote:
> On Thu, 10 Sep 2015, Dmitry Vyukov wrote:
>
>> On Thu, Sep 10, 2015 at 8:01 PM, Christoph Lameter <cl@linux.com> wrote:
>> > On Thu, 10 Sep 2015, Paul E. McKenney wrote:
>> >
>> >> The reason we poked at this was to see if any of SLxB touched the
>> >> memory being freed.  If none of them touched the memory being freed,
>> >> and if that was a policy, then the idiom above would be legal.  However,
>> >> one of them does touch the memory being freed, so, yes, the above code
>> >> needs to be fixed.
>> >
>> > The one that touches the object has a barrier() before it touches the
>> > memory.
>>
>> It does not change anything, right?
>
> It changes the first word of the object after the barrier. The first word
> is used in SLUB as the pointer to the next free object.

User can also write to this object after it is reallocated. It is
equivalent to kmalloc writing to the object.
And barrier is not the kind of barrier that would make it correct.
So I do not see how it is relevant.

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