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author | Jason Wessel <jason.wessel@windriver.com> | 2010-01-27 23:25:22 +0100 |
---|---|---|
committer | Ingo Molnar <mingo@elte.hu> | 2010-02-01 08:22:32 +0100 |
commit | d6ad3e286d2c075a60b9f11075a2c55aeeeca2ad (patch) | |
tree | 24f374a6cb1ef36c2aec41b9de6b8f3b1b09780d /kernel/softlockup.c | |
parent | lockdep: Fix check_usage_backwards() error message (diff) | |
download | linux-d6ad3e286d2c075a60b9f11075a2c55aeeeca2ad.tar.xz linux-d6ad3e286d2c075a60b9f11075a2c55aeeeca2ad.zip |
softlockup: Add sched_clock_tick() to avoid kernel warning on kgdb resume
When CONFIG_HAVE_UNSTABLE_SCHED_CLOCK is set, sched_clock() gets
the time from hardware such as the TSC on x86. In this
configuration kgdb will report a softlock warning message on
resuming or detaching from a debug session.
Sequence of events in the problem case:
1) "cpu sched clock" and "hardware time" are at 100 sec prior
to a call to kgdb_handle_exception()
2) Debugger waits in kgdb_handle_exception() for 80 sec and on
exit the following is called ... touch_softlockup_watchdog() -->
__raw_get_cpu_var(touch_timestamp) = 0;
3) "cpu sched clock" = 100s (it was not updated, because the
interrupt was disabled in kgdb) but the "hardware time" = 180 sec
4) The first timer interrupt after resuming from
kgdb_handle_exception updates the watchdog from the "cpu sched clock"
update_process_times() { ... run_local_timers() -->
softlockup_tick() --> check (touch_timestamp == 0) (it is "YES"
here, we have set "touch_timestamp = 0" at kgdb) -->
__touch_softlockup_watchdog() ***(A)--> reset "touch_timestamp"
to "get_timestamp()" (Here, the "touch_timestamp" will still be
set to 100s.) ...
scheduler_tick() ***(B)--> sched_clock_tick() (update "cpu sched
clock" to "hardware time" = 180s) ... }
5) The Second timer interrupt handler appears to have a large
jump and trips the softlockup warning.
update_process_times() { ... run_local_timers() -->
softlockup_tick() --> "cpu sched clock" - "touch_timestamp" =
180s-100s > 60s --> printk "soft lockup error messages" ... }
note: ***(A) reset "touch_timestamp" to
"get_timestamp(this_cpu)"
Why is "touch_timestamp" 100 sec, instead of 180 sec?
When CONFIG_HAVE_UNSTABLE_SCHED_CLOCK is set, the call trace of
get_timestamp() is:
get_timestamp(this_cpu)
-->cpu_clock(this_cpu)
-->sched_clock_cpu(this_cpu)
-->__update_sched_clock(sched_clock_data, now)
The __update_sched_clock() function uses the GTOD tick value to
create a window to normalize the "now" values. So if "now"
value is too big for sched_clock_data, it will be ignored.
The fix is to invoke sched_clock_tick() to update "cpu sched
clock" in order to recover from this state. This is done by
introducing the function touch_softlockup_watchdog_sync(). This
allows kgdb to request that the sched clock is updated when the
watchdog thread runs the first time after a resume from kgdb.
[yong.zhang0@gmail.com: Use per cpu instead of an array]
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Dongdong Deng <Dongdong.Deng@windriver.com>
Cc: kgdb-bugreport@lists.sourceforge.net
Cc: peterz@infradead.org
LKML-Reference: <1264631124-4837-2-git-send-email-jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/softlockup.c')
-rw-r--r-- | kernel/softlockup.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/kernel/softlockup.c b/kernel/softlockup.c index d22579087e27..0d4c7898ab80 100644 --- a/kernel/softlockup.c +++ b/kernel/softlockup.c @@ -25,6 +25,7 @@ static DEFINE_SPINLOCK(print_lock); static DEFINE_PER_CPU(unsigned long, softlockup_touch_ts); /* touch timestamp */ static DEFINE_PER_CPU(unsigned long, softlockup_print_ts); /* print timestamp */ static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog); +static DEFINE_PER_CPU(bool, softlock_touch_sync); static int __read_mostly did_panic; int __read_mostly softlockup_thresh = 60; @@ -79,6 +80,12 @@ void touch_softlockup_watchdog(void) } EXPORT_SYMBOL(touch_softlockup_watchdog); +void touch_softlockup_watchdog_sync(void) +{ + __raw_get_cpu_var(softlock_touch_sync) = true; + __raw_get_cpu_var(softlockup_touch_ts) = 0; +} + void touch_all_softlockup_watchdogs(void) { int cpu; @@ -118,6 +125,14 @@ void softlockup_tick(void) } if (touch_ts == 0) { + if (unlikely(per_cpu(softlock_touch_sync, this_cpu))) { + /* + * If the time stamp was touched atomically + * make sure the scheduler tick is up to date. + */ + per_cpu(softlock_touch_sync, this_cpu) = false; + sched_clock_tick(); + } __touch_softlockup_watchdog(); return; } |