Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936122AbcJUXJa (ORCPT ); Fri, 21 Oct 2016 19:09:30 -0400 Received: from mail-pf0-f169.google.com ([209.85.192.169]:34533 "EHLO mail-pf0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932774AbcJUXJ3 (ORCPT ); Fri, 21 Oct 2016 19:09:29 -0400 From: Douglas Anderson To: Jason Wessel Cc: Daniel Thompson , Andrew Morton , briannorris@chromium.org, Douglas Anderson , kgdb-bugreport@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: [PATCH v2] debug: More properly delay for secondary CPUs Date: Fri, 21 Oct 2016 16:09:21 -0700 Message-Id: <1477091361-2039-1-git-send-email-dianders@chromium.org> X-Mailer: git-send-email 2.8.0.rc3.226.g39d4020 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1824 Lines: 53 We've got a delay loop waiting for secondary CPUs. That loop uses loops_per_jiffy. However, loops_per_jiffy doesn't actually mean how many tight loops make up a jiffy on all architectures. It is quite common to see things like this in the boot log: Calibrating delay loop (skipped), value calculated using timer frequency.. 48.00 BogoMIPS (lpj=24000) In my case I was seeing lots of cases where other CPUs timed out entering the debugger only to print their stack crawls shortly after the kdb> prompt was written. Elsewhere in kgdb we already use udelay(), so that should be safe enough to use to implement our timeout. We'll delay 1 ms for 1000 times, which should give us a full second of delay (just like the old code wanted) but allow us to notice that we're done every 1 ms. Signed-off-by: Douglas Anderson --- Changes in v2: - Use udelay, not __delay kernel/debug/debug_core.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c index 0874e2edd275..85a246feb442 100644 --- a/kernel/debug/debug_core.c +++ b/kernel/debug/debug_core.c @@ -61,6 +61,8 @@ #include "debug_core.h" +#define WAIT_CPUS_STOP_MS 1000 + static int kgdb_break_asap; struct debuggerinfo_struct kgdb_info[NR_CPUS]; @@ -598,11 +600,11 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs, /* * Wait for the other CPUs to be notified and be waiting for us: */ - time_left = loops_per_jiffy * HZ; + time_left = WAIT_CPUS_STOP_MS; while (kgdb_do_roundup && --time_left && (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) != online_cpus) - cpu_relax(); + udelay(1000); if (!time_left) pr_crit("Timed out waiting for secondary CPUs.\n"); -- 2.8.0.rc3.226.g39d4020