sequence lock in Linux

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Hi Paul,

(CCing lkml)

Is it just me, or the following code:

static __always_inline unsigned read_seqbegin(const seqlock_t *sl)
{
        unsigned ret;

repeat:
        ret = sl->sequence;
        smp_rmb();
        if (unlikely(ret & 1)) {
                cpu_relax();
                goto repeat;
        }

        return ret;
}

could use a ACCESS_ONCE() around the sl->sequence read ? I'm concerned about the
compiler generating code that reads the sequence number chunkwise.

The same apply to all other reads of the sequence number in seqlock.h (including
the retry code).

Thoughts ?

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com