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    Subject[PATCH v3 tip/core/rcu 02/40] rcu: Make arch select smp_mb__after_unlock_lock() strength
    Date
    The definition of smp_mb__after_unlock_lock() is currently smp_mb()
    for CONFIG_PPC and a no-op otherwise. It would be better to instead
    provide an architecture-selectable Kconfig option, and select the
    strength of smp_mb__after_unlock_lock() based on that option. This
    commit therefore creates ARCH_WEAK_RELEASE_ACQUIRE, has PPC select it,
    and bases the definition of smp_mb__after_unlock_lock() on this new
    ARCH_WEAK_RELEASE_ACQUIRE Kconfig option.

    Reported-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Boqun Feng <boqun.feng@linux.vnet.ibm.com>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Acked-by: Michael Ellerman <mpe@ellerman.id.au>
    Cc: <linuxppc-dev@lists.ozlabs.org>
    Reviewed-by: Josh Triplett <josh@joshtriplett.org>
    ---
    arch/Kconfig | 3 +++
    arch/powerpc/Kconfig | 1 +
    include/linux/rcupdate.h | 6 +++---
    3 files changed, 7 insertions(+), 3 deletions(-)

    diff --git a/arch/Kconfig b/arch/Kconfig
    index cd211a14a88f..adefaf344239 100644
    --- a/arch/Kconfig
    +++ b/arch/Kconfig
    @@ -320,6 +320,9 @@ config HAVE_CMPXCHG_LOCAL
    config HAVE_CMPXCHG_DOUBLE
    bool

    +config ARCH_WEAK_RELEASE_ACQUIRE
    + bool
    +
    config ARCH_WANT_IPC_PARSE_VERSION
    bool

    diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
    index 97a8bc8a095c..7a5c9b764cd2 100644
    --- a/arch/powerpc/Kconfig
    +++ b/arch/powerpc/Kconfig
    @@ -99,6 +99,7 @@ config PPC
    select ARCH_USE_BUILTIN_BSWAP
    select ARCH_USE_CMPXCHG_LOCKREF if PPC64
    select ARCH_WANT_IPC_PARSE_VERSION
    + select ARCH_WEAK_RELEASE_ACQUIRE
    select BINFMT_ELF
    select BUILDTIME_EXTABLE_SORT
    select CLONE_BACKWARDS
    diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    index de88b33c0974..e6146d0074f8 100644
    --- a/include/linux/rcupdate.h
    +++ b/include/linux/rcupdate.h
    @@ -1127,11 +1127,11 @@ do { \
    * if the UNLOCK and LOCK are executed by the same CPU or if the
    * UNLOCK and LOCK operate on the same lock variable.
    */
    -#ifdef CONFIG_PPC
    +#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
    #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
    -#else /* #ifdef CONFIG_PPC */
    +#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
    #define smp_mb__after_unlock_lock() do { } while (0)
    -#endif /* #else #ifdef CONFIG_PPC */
    +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */


    #endif /* __LINUX_RCUPDATE_H */
    --
    2.5.2
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