On Mon, Oct 10, 2016 at 15:59:04 +0200, Paolo Bonzini wrote: > There is a data race if the variable is written concurrently to the > read. In C11 this has undefined behavior. Use atomic_read. The > write side does not need atomic_set, because it is protected by a > mutex.
Is tsan happy with the way seqlocks are written right now? According to this message I just found by Dmitry Vyukov, tsan shouldn't be. Note however that the message is from April'15, so it might be outdated: Dmitry Vyukov wrote: > 1. Tsan is bad at handling stand-alone memory barriers. <snip> > And here is a way to express seqlock that is both correct, is > understood by tsan and is no overhead on x86: > > // writer > atomic_store(&seq, seq+1, memory_order_relaxed); > atomic_store(&data[0], ..., memory_order_release); > ... > atomic_store(&data[N], ..., memory_order_release); > atomic_store(&seq, seq+1, memory_order_release); > > // reader > atomic_load(&seq, memory_order_acquire); > d0 = atomic_load(&data[0], memory_order_acquire); > ... > dN = atomic_load(&data[N], memory_order_acquire); > atomic_load(&seq, memory_order_relaxed); Source: https://groups.google.com/forum/#!topic/thread-sanitizer/B4i9EMQ4BQE Thanks, Emilio
