Re: [PATCH v3 2/4] membarrier: Add an actual barrier before rseq_preempt()

On Thu, Dec 3, 2020 at 9:07 PM Andy Lutomirski luto@kernel.org wrote:

It seems to me that most RSEQ membarrier users will expect any stores done before the membarrier() syscall to be visible to the target task(s). While this is extremely likely to be true in practice, nothing actually guarantees it by a strict reading of the x86 manuals. Rather than providing this guarantee by accident and potentially causing a problem down the road, just add an explicit barrier.

Cc: stable@vger.kernel.org

Fixes: 2a36ab717e8f ("rseq/membarrier: Add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ")

which is new in 5.10, so it doesn't need cc:stable if it makes 5.10.