This is a note to let you know that I've just added the patch titled
kernel/debug/debug_core.c: more properly delay for secondary CPUs
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kernel-debug-debug_core.c-more-properly-delay-for-secondary-cpus.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2d13bb6494c807bcf3f78af0e96c0b8615a94385 Mon Sep 17 00:00:00 2001
From: Douglas Anderson <dianders@xxxxxxxxxxxx>
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@xxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxx: simplifications, per Daniel]
Link: http://lkml.kernel.org/r/1477091361-2039-1-git-send-email-dianders@xxxxxxxxxxxx
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
Cc: Brian Norris <briannorris@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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");
Patches currently in stable-queue which might be from dianders@xxxxxxxxxxxx are
queue-4.9/kernel-debug-debug_core.c-more-properly-delay-for-secondary-cpus.patch
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