The patch titled
Subject: kernel/debug/debug_core.c: more properly delay for secondary CPUs
has been added to the -mm tree. Its filename is
debug-more-properly-delay-for-secondary-cpus.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/debug-more-properly-delay-for-secondary-cpus.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/debug-more-properly-delay-for-secondary-cpus.patch
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From: Douglas Anderson <dianders@xxxxxxxxxxxx>
Subject: kernel/debug/debug_core.c: more properly delay for secondary CPUs
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.
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>
Cc: <stable@xxxxxxxxxxxxxxx> [4.0+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/debug/debug_core.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN kernel/debug/debug_core.c~debug-more-properly-delay-for-secondary-cpus kernel/debug/debug_core.c
--- a/kernel/debug/debug_core.c~debug-more-properly-delay-for-secondary-cpus
+++ a/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 @@ return_normal:
/*
* 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");
_
Patches currently in -mm which might be from dianders@xxxxxxxxxxxx are
debug-more-properly-delay-for-secondary-cpus.patch
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