On Wed, Dec 9, 2020 at 12:42 AM tip-bot2 for Andy Lutomirski tip-bot2@linutronix.de wrote:
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 2ecedd7569080fd05c1a457e8af2165afecfa29f Gitweb: https://git.kernel.org/tip/2ecedd7569080fd05c1a457e8af2165afecfa29f Author: Andy Lutomirski luto@kernel.org AuthorDate: Thu, 03 Dec 2020 21:07:04 -08:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Wed, 09 Dec 2020 09:37:43 +01:00
membarrier: Add an actual barrier before rseq_preempt()
It seems 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.
Fixes: 70216e18e519 ("membarrier: Provide core serializing command, *_SYNC_CORE")
Whoops, this got mangled on its way to tip. This should be:
Fixes: 2a36ab717e8f ("rseq/membarrier: Add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ")
and this patch does not need to be backported.