On Thu, Sep 1, 2016 at 7:01 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: > > > On 01/09/2016 00:29, Pranith Kumar wrote: >> smp_read_barrier_depends() should be used only if you are reading >> dependent pointers which are shared. > > bh is shared since it is equal to ctx->first_bh or > ctx->first_bh->...->next. While the compiler will always order the load > of bh->next after the load of ctx->first_bh and any previous load of > bh->next, this may not be the case for the processor. Only the DEC > Alpha has this behavior, but it _can_ happen.
In that case there are a bunch of places in the same file where we need to insert this barrier. I also guarantee that there are many more files which would need this barrier if we examine closely. I really doubt if we see this kind of re-ordering. Did we ever get any bug reports about running qemu on an SMP Alpha? smp_read_barrier_depends() is evil and I would prefer we get rid of it. Thanks, -- Pranith
