----- On Nov 16, 2020, at 6:57 PM, Andy Lutomirski luto@xxxxxxxxxx wrote: > Linux 5.10 contains this patch: > > commit 2a36ab717e8fe678d98f81c14a0b124712719840 > Author: Peter Oskolkov <posk@xxxxxxxxxx> > Date: Wed Sep 23 16:36:16 2020 -0700 > > rseq/membarrier: Add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ > > This adds an argument to an existing syscall. Before the patch, > membarrier had 2 parameters; now it has 3. Is this really okay? At > least the patch is careful and ignores the third parameter unless a > previously unused flag bit is set. Hi Andy, I wondered about exactly this on August 12 2020: https://lore.kernel.org/r/1477195446.6156.1597261492255.JavaMail.zimbra@xxxxxxxxxxxx And then on August 25, after receiving no feedback, I told Peter to try this approach: https://lore.kernel.org/r/1336467655.17779.1598374701401.JavaMail.zimbra@xxxxxxxxxxxx and nobody complained until now. As you note, the extra argument is only used when previously unused flag bits are set. So your question is very relevant, and I still look forward to receiving feedback on this matter. Thanks, Mathieu > > --Andy -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
