[Boost-bugs] [Boost C++ Libraries] #11362: smart_ptr spinlocks leads to livelock on ARM Cortex-A9 CPUs

Subject: [Boost-bugs] [Boost C++ Libraries] #11362: smart_ptr spinlocks leads to livelock on ARM Cortex-A9 CPUs
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-05-29 19:10:00

#11362: smart_ptr spinlocks leads to livelock on ARM Cortex-A9 CPUs
------------------------------+-----------------------
 Reporter:  alex              |      Owner:  pdimov
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  smart_ptr
  Version:  Boost 1.57.0      |   Severity:  Problem
 Keywords:  arm spinlock      |
------------------------------+-----------------------
 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.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11362>
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