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;