[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20200811062733.GP3982@worktop.programming.kicks-ass.net>
Date: Tue, 11 Aug 2020 08:27:33 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Peter Oskolkov <posk@...gle.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
"Paul E . McKenney" <paulmck@...nel.org>,
Boqun Feng <boqun.feng@...il.com>,
linux-kernel@...r.kernel.org, Paul Turner <pjt@...gle.com>,
Chris Kennelly <ckennelly@...gle.com>,
Peter Oskolkov <posk@...k.io>
Subject: Re: [PATCH 1/2 v3] rseq/membarrier: add
MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ
On Mon, Aug 10, 2020 at 05:09:58PM -0700, Peter Oskolkov wrote:
> @@ -27,6 +35,12 @@
>
> static void ipi_mb(void *info)
> {
The #ifdef wants to behere, otherwise you'll get a compile warning for
!RSEQ builds.
> + int *flags = info;
> +
> +#ifdef CONFIG_RSEQ
> + if (flags && (*flags == MEMBARRIER_FLAG_RSEQ))
> + rseq_preempt(current);
> +#endif
> smp_mb(); /* IPIs should be serializing but paranoid. */
> }
But yes, this looks much better.
Mathieu did mention a few other points that I didn't see addressed:
- he didn't like abusing the @flags syscall argument for a CPUid;
- he wondered if we should support SYNC_CORE + RSEQ.
Not sure we can easily change the syscall at this point, but the latter
point could be addressed with something like this.
---
Index: linux-2.6/kernel/sched/membarrier.c
===================================================================
--- linux-2.6.orig/kernel/sched/membarrier.c
+++ linux-2.6/kernel/sched/membarrier.c
@@ -374,8 +374,26 @@ static int membarrier_register_private_e
*/
SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
{
+ int cflags = 0, int cpuid = -1;
+
if (unlikely(flags) && cmd != MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ)
return -EINVAL;
+
+ if (cmd & (MEMBARRIER_CMD_PRIVATE_EXPEDITED |
+ MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE |
+ MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ)) {
+
+ if (cmd & MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ)
+ cflags |= MEMBARRIER_FLAG_RSEQ;
+
+ if (cmd & MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE) {
+ cflags |= MEMBARRIER_FLAG_SYNC_CORE;
+ cpuid = flags;
+ }
+
+ cmd = MEMBARRIER_CMD_PRIVATE_EXPEDITED;
+ }
+
switch (cmd) {
case MEMBARRIER_CMD_QUERY:
{
@@ -396,18 +414,16 @@ SYSCALL_DEFINE2(membarrier, int, cmd, in
return membarrier_global_expedited();
case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
return membarrier_register_global_expedited();
- case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
- return membarrier_private_expedited(0, -1);
case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
return membarrier_register_private_expedited(0);
- case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
- return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE, -1);
case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
- case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ:
- return membarrier_private_expedited(MEMBARRIER_FLAG_RSEQ, flags);
case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ:
return membarrier_register_private_expedited(MEMBARRIER_FLAG_RSEQ);
+
+ case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
+ return membarrier_private_expedited(cflags, cpuid);
+
default:
return -EINVAL;
}
Powered by blists - more mailing lists