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    Subject[PATCH 4.14 023/193] MIPS: cmpxchg64() and HAVE_VIRT_CPU_ACCOUNTING_GEN dont work for 32-bit SMP
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Ben Hutchings <ben@decadent.org.uk>

    commit a3f143106596d739e7fbc4b84c96b1475247d876 upstream.

    __cmpxchg64_local_generic() is atomic only w.r.t tasks and interrupts
    on the same CPU (that's what the 'local' means). We can't use it to
    implement cmpxchg64() in SMP configurations.

    So, for 32-bit SMP configurations:

    - Don't define cmpxchg64()
    - Don't enable HAVE_VIRT_CPU_ACCOUNTING_GEN, which requires it

    Fixes: e2093c7b03c1 ("MIPS: Fall back to generic implementation of ...")
    Fixes: bb877e96bea1 ("MIPS: Add support for full dynticks CPU time accounting")
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Cc: Deng-Cheng Zhu <dengcheng.zhu@mips.com>
    Cc: linux-mips@linux-mips.org
    Patchwork: https://patchwork.linux-mips.org/patch/17413/
    Signed-off-by: James Hogan <jhogan@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/mips/Kconfig | 2 +-
    arch/mips/include/asm/cmpxchg.h | 2 ++
    2 files changed, 3 insertions(+), 1 deletion(-)

    --- a/arch/mips/Kconfig
    +++ b/arch/mips/Kconfig
    @@ -65,7 +65,7 @@ config MIPS
    select HAVE_PERF_EVENTS
    select HAVE_REGS_AND_STACK_ACCESS_API
    select HAVE_SYSCALL_TRACEPOINTS
    - select HAVE_VIRT_CPU_ACCOUNTING_GEN
    + select HAVE_VIRT_CPU_ACCOUNTING_GEN if 64BIT || !SMP
    select IRQ_FORCED_THREADING
    select MODULES_USE_ELF_RELA if MODULES && 64BIT
    select MODULES_USE_ELF_REL if MODULES
    --- a/arch/mips/include/asm/cmpxchg.h
    +++ b/arch/mips/include/asm/cmpxchg.h
    @@ -204,8 +204,10 @@ static inline unsigned long __cmpxchg(vo
    #else
    #include <asm-generic/cmpxchg-local.h>
    #define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
    +#ifndef CONFIG_SMP
    #define cmpxchg64(ptr, o, n) cmpxchg64_local((ptr), (o), (n))
    #endif
    +#endif

    #undef __scbeqz


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