On Wed, 3 Apr 2013, Linus Torvalds wrote: > Any compiler that thinks it can load something through a "volatile" > pointer multiple times is SHIT. We don't add these kinds of comments > to make excuses for crap, we call out such compilers and tell people > not to use the utter crap they are. > How nice to have reconvened after six years when in February of 2007 you slammed me for relying on the implementation of a particular compiler on the sign of a bitfield and referred multiple times to the standard and how it's implementation defined. I don't want to go down that road again, even though the poster of quotes we had on the wall at work was amusing for awhile. The specification here says an access to this volatile quaified pointer is implementation defined. It also allows for the pointer to be reloaded and the local variable optimized out. Do people need to know that? Debatable. But there are misconceptions of what a volatile-qualified pointer can do. This patch was an attempt to clarify for those who didn't understand that we're relying on the implementation of the compiler to not optimize the loads from memory out. The way the comment is currently written, stating that it is "preventing the compiler from refetching" can literally mean one of two things: it actually does something based on specification that causes these objects to not be reloaded, or it is using the way volatile-qualified pointers are dereferenced in gcc and other compilers to prevent it. I'm pretty darn sure Paul was referring to the latter when he wrote it, which is completely 100% correct, but other readers of the comment have taken it to mean the former and it causes misconceptions of the keyword. That said, I'm not interested in arguing with you on the meaning of the word "prevent" in the ACCESS_ONCE() comment nor in the changelog of the patch that sparked this discussion. We're talking about English here, not C, and the goal was to make it explicit. If you take offense to that, owell. Ian has suggested that we file a request with the gcc team for the exact semantics we're asking for from ACCESS_ONCE() so that we don't need to rely on any particular compiler's implementation and can standardize this at least for gcc. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>