This grsecurity blog entry looks at how an ineffective Spectre fix found its way into the stable kernel releases. If one looks past the advertising, it's a good summary of how the kernel processes can produce the wrong result. "Despite this warning, this code was merged into Thomas Gleixner's x86/tip tree verbatim, as can be seen here. Prior to merging the fix for 5.3-rc1, Linus Torvalds noticed the warning as seen on the LKML mailing list here and fixed it correctly. However, when the actual merge of the tree was performed, no mention was made of the correction to the fix, and with no specific commit mentioning the correction and fixing it alone, everyone else's processes that depended on cherry-picking specific commits ended up grabbing the bad warning-inducing change. As a further failure, instead of looking at Linus' correct fix (observable by checking out the master tree at the time), the approach seems to have been to naively silence the warning by simply swapping the order of the two lines."