| From 2d13bb6494c807bcf3f78af0e96c0b8615a94385 Mon Sep 17 00:00:00 2001 |
| From: Douglas Anderson <dianders@chromium.org> |
| Date: Wed, 14 Dec 2016 15:05:49 -0800 |
| Subject: kernel/debug/debug_core.c: more properly delay for secondary CPUs |
| |
| From: Douglas Anderson <dianders@chromium.org> |
| |
| commit 2d13bb6494c807bcf3f78af0e96c0b8615a94385 upstream. |
| |
| 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. |
| |
| [akpm@linux-foundation.org: simplifications, per Daniel] |
| Link: http://lkml.kernel.org/r/1477091361-2039-1-git-send-email-dianders@chromium.org |
| Signed-off-by: Douglas Anderson <dianders@chromium.org> |
| Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org> |
| Cc: Jason Wessel <jason.wessel@windriver.com> |
| Cc: Brian Norris <briannorris@chromium.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| kernel/debug/debug_core.c | 4 ++-- |
| 1 file changed, 2 insertions(+), 2 deletions(-) |
| |
| --- a/kernel/debug/debug_core.c |
| +++ b/kernel/debug/debug_core.c |
| @@ -598,11 +598,11 @@ return_normal: |
| /* |
| * Wait for the other CPUs to be notified and be waiting for us: |
| */ |
| - time_left = loops_per_jiffy * HZ; |
| + time_left = MSEC_PER_SEC; |
| 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"); |
| |