On 20/01/15 20:53, Stephen Boyd wrote:
> On 01/20/2015 02:25 AM, Daniel Thompson wrote:
>> On 13/01/15 10:26, Daniel Thompson wrote:
>>> Hi Thomas, Hi Jason:
>>> Patches 1 to 3 are for you (and should be separable from the rest
>>> of the series). The patches haven't changes since the last time
>>> I posted them. The changes in v14 tidy up the later part of the
>>> patch set in order to share more code between x86 and arm.
>> No review comments! Have I finally got this right?
>>
>> If so it possible and/or sensible to get patches 1-3 in a tree that
>> feeds linux-next. I'd really like the gic changes to meet the various
>> ARM build and boot bots.
>
> With this patchset, is it possible to call sched_clock() from within NMI
> context? I ask because the generic sched_clock() code is not NMI safe
> today. We were planning on making it NMI safe by doing something similar
> to what was done for ktime_get_mono_fast_ns() but we haven't gotten
> around to it. Mostly because no architecture that uses generic
> sched_clock() has support for NMIs right now.
I've not done any work to make sched_clock() safe to call from NMI.
However since my patchset does not introduce any calls to sched_clock()
from NMI I think this is OK!
I ported Steven Rostedt's work to make arch_trigger_all_cpu_backtrace()
safe from NMI from x86 to ARM. One result of Steven's approach are that
printk() timestamping is deferred until we return to normal context.
Thus even with CONFIG_PRINTK_TIME we do not call local_clock() during
NMI processing.
To confirm the above I have added the code below to my kernel and ran it
with a fairly paranoid set of debugging options. The check does not fire.
Daniel.
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 630dd2372238..fea0deeb524b 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -111,8 +111,10 @@ extern void warn_slowpath_null(const char *file,
const int line);
int __ret_warn_once = !!(condition); \
\
if (unlikely(__ret_warn_once)) \
- if (WARN_ON(!__warned)) \
+ if (unlikely(!__warned)) { \
__warned = true; \
+ __WARN(); \
+ } \
unlikely(__ret_warn_once); \
})
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index 01d2d15aa662..81ea469b7e68 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -63,6 +63,8 @@ unsigned long long notrace sched_clock(void)
u64 cyc;
unsigned long seq;
+ WARN_ON_ONCE(in_nmi());
+
if (cd.suspended)
return cd.epoch_ns;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
