id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
11362	smart_ptr spinlocks leads to livelock on ARM Cortex-A9 CPUs	alex	Peter Dimov	"Spinlock used in smart_ptr for ARM architecture (smart_ptr/details/spinlock_gcc_arm.hpp) relies on swp/mcr instruction sequence or ldrex/strex/dmb depending on ARM version. Both these implementations are affected by an ARM issue described in errata 754327 for ARM Cortex-A9 CPU.

Suggested fix is to add ""dmb"" instruction to change spinlock::unlock() method:

    void unlock()
    {
        __asm__ __volatile__( BOOST_SP_ARM_BARRIER ::: ""memory"" );
        *const_cast< int volatile* >( &v_ ) = 0;
        __asm__ __volatile__( BOOST_SP_ARM_BARRIER ::: ""memory"" );
    }

Second barrier was added as recommended workaround from ARM errata document."	Bugs	closed	To Be Determined	smart_ptr	Boost 1.57.0	Problem	fixed	arm spinlock