From: Paul E. McKenney

Sent: 20 November 2017 20:54

On Mon, Nov 20, 2017 at 08:32:56PM +0100, Peter Zijlstra wrote:

quoted

On Mon, Nov 20, 2017 at 06:05:55PM +0000, Will Deacon wrote:

quoted

Although the current direction of the C++ committee is to prefer
that dependencies are explicitly "marked", this is not deemed to be
acceptable for the kernel (in other words, everything is always considered
"marked").

Yeah, that is an attitude not compatible with existing code. Much like
the proposal to allow temporary/wide stores on everything not explicitly
declared atomic. Such stuff instantly breaks all extant code that does
multi-threading with no recourse.

If someone suggests temporary/wide stores, even on non-atomics, tell
them that the standard does not permit them to introduce data races.

The C standard doesn't say anything about multi-threading.

The x86 bis (bit set) family are well known for being problematic
because they always do a 32bit wide rmw cycle.

	David