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    SubjectRe: [PATCH] fib_trie: rcu_assign_pointer warning fix
    On 12-02-2008 02:16, David Miller wrote:
    > From: Stephen Hemminger <shemminger@vyatta.com>
    > Date: Mon, 11 Feb 2008 16:59:54 -0800
    >
    > linux-kernel added to CC:, any change to generic kernel infrastructure
    > should be posted there
    >
    >> Eliminate warnings when rcu_assign_pointer is used with unsigned long.
    >> It is reasonable to use RCU with non-pointer values so allow it for general
    >> use. Add a comment to explain the if test.
    >>
    >> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
    >> ---
    >> include/linux/rcupdate.h | 13 +++++++------
    >> 1 files changed, 7 insertions(+), 6 deletions(-)
    >>
    >> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    >> index 37a642c..c44ac87 100644
    >> --- a/include/linux/rcupdate.h
    >> +++ b/include/linux/rcupdate.h
    >> @@ -172,14 +172,15 @@ struct rcu_head {
    >> * structure after the pointer assignment. More importantly, this
    >> * call documents which pointers will be dereferenced by RCU read-side
    >> * code.
    >> + *
    >> + * If value is the NULL (constant 0), then no barrier is needed.
    >> */
    >>
    >> -#define rcu_assign_pointer(p, v) \
    >> - ({ \
    >> - if (!__builtin_constant_p(v) || \
    >> - ((v) != NULL)) \
    >> - smp_wmb(); \
    >> - (p) = (v); \
    >> +#define rcu_assign_pointer(p, v) \
    >> + ({ \
    >> + if (!(__builtin_constant_p(v) && v)) \

    ...But, "If value is the NULL (constant 0)" we have:

    if (!(1 && NULL != 0)) ==> if (!(0)) and the barrier is used?!

    >> + smp_wmb(); \
    >> + (p) = (v); \
    >> })
    >>
    >> /**


    Regards,
    Jarek P.


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