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    SubjectRe: Uninline kcalloc
    On Tue, 14 Feb 2012, Nick Bowler wrote:

    > On 2012-02-14 13:37 -0600, Christoph Lameter wrote:
    > > This patch still preserves kcalloc. But note that if kcalloc returns NULL
    > > then multiple conditions may have caused it. One is that the array is
    > > simply too large. The other may be that such an allocation is not possible
    > > due to fragmentation.
    > [...]
    > > +static inline long calculate_array_size(size_t n, size_t size)
    > > +{
    > > + if (size != 0 && n > ULONG_MAX / size)
    > > +
    > > + return 0;
    >
    > This isn't right. The above tests whether or not the result of the
    > multiplication will not be representable in an 'unsigned long'...

    Yes and so does the current kcalloc.

    > > + return n * size;
    >
    > but then the result is assigned to a (signed) long, which may overflow
    > if it's greater than LONG_MAX.

    That can happen? But you are right its better to use the size_t as the
    result of the argument. There is a gooh of long / size_t confusion
    already. This useless function should not be in the kernel.


    > > +}
    > [...]
    > > void *kcalloc(size_t n, size_t size, gfp_t flags)
    > > {
    > > - if (size != 0 && n > ULONG_MAX / size)
    > > - return NULL;
    > > - return __kmalloc(n * size, flags | __GFP_ZERO);
    > > + size_t s = calculate_array_size(n, size);
    > > +
    > > + if (s)
    > > + return kzalloc(s, flags);
    > > +
    > > + return NULL;
    > > }
    >
    > This hunk changes the behaviour of kcalloc if either of the two size parameters
    > is 0.

    You want ZERO_PTR returns?

    NULL is one permissible return value of calloc() if size == 0. So we are
    now deviating from user space conventions.



    Subject: Introduce calculate_array_size

    calculate_array_size calculates the size of an array while
    checking for errors. Returns 0 if the size is too large.

    Signed-off-by: Christoph Lameter <cl@linux.com>


    ---
    include/linux/slab.h | 15 +++++++++++++++
    mm/util.c | 7 +++++--
    2 files changed, 20 insertions(+), 2 deletions(-)

    Index: linux-2.6/include/linux/slab.h
    ===================================================================
    --- linux-2.6.orig/include/linux/slab.h 2012-02-14 15:16:53.000000000 -0600
    +++ linux-2.6/include/linux/slab.h 2012-02-14 15:21:39.000000000 -0600
    @@ -242,6 +242,21 @@ size_t ksize(const void *);
    */
    void *kcalloc(size_t n, size_t size, gfp_t flags);

    +/*
    + * calculate_array_size - Calculate an array size given the size of a
    + * particular element with checking for overflow.
    + *
    + * Return 0 if there is an overflow.
    + */
    +static inline size_t calculate_array_size(size_t n, size_t size)
    +{
    + if (n > ULONG_MAX / size)
    +
    + return 0;
    +
    + return n * size;
    +}
    +
    #if !defined(CONFIG_NUMA) && !defined(CONFIG_SLOB)
    /**
    * kmalloc_node - allocate memory from a specific node
    Index: linux-2.6/mm/util.c
    ===================================================================
    --- linux-2.6.orig/mm/util.c 2012-02-14 15:16:53.000000000 -0600
    +++ linux-2.6/mm/util.c 2012-02-14 15:21:05.000000000 -0600
    @@ -83,9 +83,12 @@ EXPORT_SYMBOL(kmemdup);
    */
    void *kcalloc(size_t n, size_t size, gfp_t flags)
    {
    - if (size != 0 && n > ULONG_MAX / size)
    + size_t s = calculate_array_size(n, size);
    +
    + if (size && !s)
    return NULL;
    - return __kmalloc(n * size, flags | __GFP_ZERO);
    +
    + return kzalloc(s, flags);
    }
    EXPORT_SYMBOL(kcalloc);


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