search for: rcu_derefer

...p_read_barrier_depends()" does NOTHING wrt the second write. > > Just to clarify: on alpha it adds a memory barrier, but that memory > barrier is useless. No trailing data-dependent read, so agreed, no smp_read_barrier_depends() needed. That said, I believe that we should encourage rcu_dereference*() or lockless_dereference() instead of READ_ONCE() for documentation reasons, though. > On non-alpha, it is a no-op, and obviously does nothing simply because > it generates no code. > > So if anybody believes that the "smp_read_barrier_depends()" does > something, t...

...p_read_barrier_depends()" does NOTHING wrt the second write. > > Just to clarify: on alpha it adds a memory barrier, but that memory > barrier is useless. No trailing data-dependent read, so agreed, no smp_read_barrier_depends() needed. That said, I believe that we should encourage rcu_dereference*() or lockless_dereference() instead of READ_ONCE() for documentation reasons, though. > On non-alpha, it is a no-op, and obviously does nothing simply because > it generates no code. > > So if anybody believes that the "smp_read_barrier_depends()" does > something, t...

...S. Stop perpetuating it. I already removed a >> number of bogus cases of it, and I removed the incorrect documentation >> that had this crap. > > If I understand your objection correctly, you want the above pattern > expressed either like this: > > struct foo *x = rcu_dereference(*ptr); > x->bar = 5; > > Or like this: > > struct foo *x = lockless_dereference(*ptr); > x->bar = 5; > > Or am I missing your point? You are entirely missing the point. You might as well just write it as struct foo x = READ_ONCE(*ptr)...

...S. Stop perpetuating it. I already removed a >> number of bogus cases of it, and I removed the incorrect documentation >> that had this crap. > > If I understand your objection correctly, you want the above pattern > expressed either like this: > > struct foo *x = rcu_dereference(*ptr); > x->bar = 5; > > Or like this: > > struct foo *x = lockless_dereference(*ptr); > x->bar = 5; > > Or am I missing your point? You are entirely missing the point. You might as well just write it as struct foo x = READ_ONCE(*ptr)...

...does NOTHING wrt the second write. > > > > Just to clarify: on alpha it adds a memory barrier, but that memory > > barrier is useless. > > No trailing data-dependent read, so agreed, no smp_read_barrier_depends() > needed. That said, I believe that we should encourage rcu_dereference*() > or lockless_dereference() instead of READ_ONCE() for documentation > reasons, though. > > > On non-alpha, it is a no-op, and obviously does nothing simply because > > it generates no code. > > > > So if anybody believes that the "smp_read_barrier_dep...

On Tue, Jan 26, 2016 at 2:15 PM, Linus Torvalds <torvalds at linux-foundation.org> wrote: > > You might as well just write it as > > struct foo x = READ_ONCE(*ptr); > x->bar = 5; > > because that "smp_read_barrier_depends()" does NOTHING wrt the second write. Just to clarify: on alpha it adds a memory barrier, but that memory barrier is useless. On

On Tue, Jan 26, 2016 at 02:33:40PM -0800, Linus Torvalds wrote: > If it turns out that some architecture does actually need a barrier > between a read and a dependent write, then that will mean that > > (a) we'll have to make up a _new_ barrier, because > "smp_read_barrier_depends()" is not that barrier. We'll presumably > then have to make that new barrier

On Tue, Jan 26, 2016 at 02:33:40PM -0800, Linus Torvalds wrote: > If it turns out that some architecture does actually need a barrier > between a read and a dependent write, then that will mean that > > (a) we'll have to make up a _new_ barrier, because > "smp_read_barrier_depends()" is not that barrier. We'll presumably > then have to make that new barrier