Since set_mb() is really about an smp_mb() -- not a IO/DMA barrier
like mb() rename it to match the recent smp_load_acquire() and
smp_store_release().
Suggested-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Since we assume set_mb() to result in a single store followed by a
full memory barrier, employ WRITE_ONCE().
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

At times where UML used the TT mode to operate it had
kind of SMP support. It never got finished nor was
stable.
Let's rip out that cruft and stop confusing developers
which do tree-wide SMP cleanups.

If someone wants SMP support UML it has do be done from scratch.
Signed-off-by: NRichard Weinberger <richard@nod.at>

... now that we have it.
Acked-by: NAndy Lutomirski <luto@amacapital.net>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: NBorislav Petkov <bp@suse.de>

There are a number of situations where the mandatory barriers rmb() and
wmb() are used to order memory/memory operations in the device drivers
and those barriers are much heavier than they actually need to be.  For
example in the case of PowerPC wmb() calls the heavy-weight sync
instruction when for coherent memory operations all that is really needed
is an lsync or eieio instruction.

This commit adds a coherent only version of the mandatory memory barriers
rmb() and wmb().  In most cases this should result in the barrier being the
same as the SMP barriers for the SMP case, however in some cases we use a
barrier that is somewhere in between rmb() and smp_rmb().  For example on
ARM the rmb barriers break down as follows:

  Barrier   Call     Explanation
  --------- -------- ----------------------------------
  rmb()     dsb()    Data synchronization barrier - system
  dma_rmb() dmb(osh) data memory barrier - outer sharable
  smp_rmb() dmb(ish) data memory barrier - inner sharable

These new barriers are not as safe as the standard rmb() and wmb().
Specifically they do not guarantee ordering between coherent and incoherent
memories.  The primary use case for these would be to enforce ordering of
reads and writes when accessing coherent memory that is shared between the
CPU and a device.

It may also be noted that there is no dma_mb().  Most architectures don't
provide a good mechanism for performing a coherent only full barrier without
resorting to the same mechanism used in mb().  As such there isn't much to
be gained in trying to define such a function.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: David Miller <davem@davemloft.net>
Acked-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NAlexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch is meant to cleanup the handling of read_barrier_depends and
smp_read_barrier_depends.  In multiple spots in the kernel headers
read_barrier_depends is defined as "do {} while (0)", however we then go
into the SMP vs non-SMP sections and have the SMP version reference
read_barrier_depends, and the non-SMP define it as yet another empty
do/while.

With this commit I went through and cleaned out the duplicate definitions
and reduced the number of definitions down to 2 per header.  In addition I
moved the 50 line comments for the macro from the x86 and mips headers that
defined it as an empty do/while to those that were actually defining the
macro, alpha and blackfin.
Signed-off-by: NAlexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This was an optimization that made memcpy type benchmarks a little
faster on ancient (Circa 1998) IDT Winchip CPUs.  In real-life
workloads, it wasn't even noticable, and I doubt anyone is running
benchmarks on 16 year old silicon any more.

Given this code has likely seen very little use over the last decade,
let's just remove it.
Signed-off-by: NDave Jones <davej@fedoraproject.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: NRichard Weinberger <richard@nod.at>
Reported-by: NToralf Förster <toralf.foerster@gmx.de>
CC: dhowells@redhat.com