When I spend more that 10 seconds in KDB console and then exit from KDB, Kernel
think that current clocksource is unstable and change it. I'm using 2.6.22-rc7
kdb on SMP i386 system. Here is log:
Before doing sync, I've set breakpoint to do_sync().
[EMAIL PROTECTED]:~#
[EMAIL PROTECTED]:~# cat
/sys/devices/system/clocksource/clocksource0/current_clocksource
tsc
[EMAIL PROTECTED]:~# sync
Instruction(i) breakpoint #0 at 0xc017b64a (adjusted)
0xc017b64a do_sync: int3
Entering kdb (current=0xc16f3a50, pid 2983) on processor 0 due to Breakpoint @
0xc017b64a
[0]kdb> go
Clocksource tsc unstable (delta = 14060902198 ns)
[EMAIL PROTECTED]:~# Time: acpi_pm clocksource has been installed.
[EMAIL PROTECTED]:~#
[EMAIL PROTECTED]:~# cat
/sys/devices/system/clocksource/clocksource0/current_clocksource
acpi_pm
[EMAIL PROTECTED]:~#
[EMAIL PROTECTED]:~#
Issue: tsc clocksource was replaced by acpi_pm.
The reason of issue:
Current clocksource(tsc) in kernel have a watchdog - another
clocksource(acpi_pm). clocksource_watchdog() that updates
watchdog_last timestamp runs with help of kernel timer that is disabled when
kernel enters kdb. So watchdog clocksource(acpi_pm) can overflow and when
kernel exits kdb, watchdog clocksource can report wrong time delta - that's why
kernel can think that current clocksource is unstable and change it.
How solved:
I suspend/resume timekeeping when we enter/exit kdb. Suspend/resume of
timekeeping suspends/resumes current clocksource and watchdog clocksource.
Also patch prevents potential softlockup warnings that appear in earlier
kernels.
Thanks.
Signed-off-by: Konstantin Baydarov <[EMAIL PROTECTED]>
kdb/kdbmain.c | 17 +++++++++++++++++
kernel/time/timekeeping.c | 27 +++++++++++++++++++++++++++
2 files changed, 44 insertions(+)
Index: linux-2.6.22-rc7/kdb/kdbmain.c
===================================================================
--- linux-2.6.22-rc7.orig/kdb/kdbmain.c
+++ linux-2.6.22-rc7/kdb/kdbmain.c
@@ -47,6 +47,9 @@
#include <asm/system.h>
#include <asm/kdebug.h>
+int kdb_timekeeping_suspend(void);
+int kdb_timekeeping_resume(void);
+
/*
* Kernel debugger state flags
*/
@@ -60,6 +63,7 @@ atomic_t kdb_8250;
*/
static DEFINE_SPINLOCK(kdb_lock);
volatile int kdb_initial_cpu = -1; /* cpu number that owns kdb */
+volatile int kdb_initial_cpu_save = -1; /* cpu number that owns
kdb */
int kdb_seqno = 2; /* how many times kdb has been
entered */
volatile int kdb_nextline = 1;
@@ -1998,6 +2002,11 @@ kdb(kdb_reason_t reason, int error, stru
smp_kdb_stop();
KDB_DEBUG_STATE("kdb 8", reason);
}
+ /* Suspend clocksource, when entering kdb, to prevent
+ * false soft lockup warnings and switching to another
+ * clocksource.
+ */
+ kdb_timekeeping_suspend();
}
if (KDB_STATE(GO1)) {
@@ -2020,6 +2029,7 @@ kdb(kdb_reason_t reason, int error, stru
if (result == KDB_CMD_GO && KDB_STATE(SSBPT))
KDB_STATE_SET(GO1);
+ kdb_initial_cpu_save = kdb_initial_cpu;
if (smp_processor_id() == kdb_initial_cpu &&
!KDB_STATE(DOING_SS) &&
!KDB_STATE(RECURSE)) {
@@ -2055,6 +2065,13 @@ kdb(kdb_reason_t reason, int error, stru
}
}
+ /* Only do this work if we are really leaving kdb */
+ if (!(KDB_STATE(DOING_SS) || KDB_STATE(SSBPT) || KDB_STATE(RECURSE))) {
+ if(smp_processor_id() == kdb_initial_cpu_save)
+ /* Resume clocksource when initial cpu leaves kdb */
+ kdb_timekeeping_resume();
+ }
+
KDB_DEBUG_STATE("kdb 14", result);
kdba_restoreint(&int_state);
#ifdef CONFIG_CPU_XSCALE
Index: linux-2.6.22-rc7/kernel/time/timekeeping.c
===================================================================
--- linux-2.6.22-rc7.orig/kernel/time/timekeeping.c
+++ linux-2.6.22-rc7/kernel/time/timekeeping.c
@@ -299,6 +299,19 @@ static int timekeeping_resume(struct sys
return 0;
}
+#if defined(CONFIG_KDB) || defined(CONFIG_KDB_MODULE)
+int kdb_timekeeping_resume(void)
+{
+ int ret;
+ struct sys_device dev;
+
+ ret = timekeeping_resume(&dev);
+
+ return ret;
+}
+EXPORT_SYMBOL(kdb_timekeeping_resume);
+#endif
+
static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
{
unsigned long flags;
@@ -313,6 +326,20 @@ static int timekeeping_suspend(struct sy
return 0;
}
+#if defined(CONFIG_KDB) || defined(CONFIG_KDB_MODULE)
+int kdb_timekeeping_suspend(void)
+{
+ int ret;
+ struct sys_device dev;
+ pm_message_t state;
+
+ ret = timekeeping_suspend(&dev, state);
+
+ return ret;
+}
+EXPORT_SYMBOL(kdb_timekeeping_suspend);
+#endif
+
/* sysfs resume/suspend bits for timekeeping */
static struct sysdev_class timekeeping_sysclass = {
.resume = timekeeping_resume,
---------------------------
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