[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h
On Thu, Jan 14, 2016 at 02:20:46PM -0800, Paul E. McKenney wrote: > On Thu, Jan 14, 2016 at 01:24:34PM -0800, Leonid Yegoshin wrote: > > On 01/14/2016 12:48 PM, Paul E. McKenney wrote: > > > > > >So SYNC_RMB is intended to implement smp_rmb(), correct? > > Yes. > > > > > >You could use SYNC_ACQUIRE() to implement read_barrier_depends() and > > >smp_read_barrier_depends(), but SYNC_RMB probably does not suffice. > > > > If smp_read_barrier_depends() is used to separate not only two reads > > but read pointer and WRITE basing on that pointer (example below) - > > yes. I just doesn't see any example of this in famous > > Documentation/memory-barriers.txt and had no chance to know what you > > use it in this way too. > > Well, Documentation/memory-barriers.txt was intended as a guide for Linux > kernel hackers, and not for hardware architects. Yeah, this goes under the header: memory-barriers.txt is _NOT_ a specification (I seem to keep repeating this). > ------------------------------------------------------------------------ > > commit 955720966e216b00613fcf60188d507c103f0e80 > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > Date: Thu Jan 14 14:17:04 2016 -0800 > > documentation: Subsequent writes ordered by rcu_dereference() > > The current memory-barriers.txt does not address the possibility of > a write to a dereferenced pointer. This should be rare, How are these rare? Isn't: rcu_read_lock() obj = rcu_dereference(ptr); if (!atomic_inc_not_zero(&obj->ref)) obj = NULL; rcu_read_unlock(); a _very_ common thing to do? _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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