Hi!
On Fri 2020-02-21 08:41:25, Greg Kroah-Hartman wrote:
From: Changbin Du changbin.du@gmail.com
[ Upstream commit 248ed51048c40d36728e70914e38bffd7821da57 ]
First, printk() is NMI-context safe now since the safe printk() has been implemented and it already has an irq_work to make NMI-context safe.
Second, this NMI irq_work actually does not work if a NMI handler causes panic by watchdog timeout. It has no chance to run in such case, while the safe printk() will flush its per-cpu buffers before panicking.
While at it, repurpose the irq_work callback into a function which concentrates the NMI duration checking and makes the code easier to follow.
I know there were printk() changes recently, but are they all in 4.19?
Does this actually fix any bug in 4.19?
Best regards, Pavel
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 086cf1d1d71d8..0f8b9b900b0e7 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -102,18 +102,22 @@ static int __init nmi_warning_debugfs(void) } fs_initcall(nmi_warning_debugfs); -static void nmi_max_handler(struct irq_work *w) +static void nmi_check_duration(struct nmiaction *action, u64 duration) {
- struct nmiaction *a = container_of(w, struct nmiaction, irq_work);
- u64 whole_msecs = READ_ONCE(action->max_duration); int remainder_ns, decimal_msecs;
- u64 whole_msecs = READ_ONCE(a->max_duration);
- if (duration < nmi_longest_ns || duration < action->max_duration)
return;- action->max_duration = duration;
remainder_ns = do_div(whole_msecs, (1000 * 1000)); decimal_msecs = remainder_ns / 1000; printk_ratelimited(KERN_INFO "INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
a->handler, whole_msecs, decimal_msecs);
action->handler, whole_msecs, decimal_msecs);} static int nmi_handle(unsigned int type, struct pt_regs *regs) @@ -140,11 +144,7 @@ static int nmi_handle(unsigned int type, struct pt_regs *regs) delta = sched_clock() - delta; trace_nmi_handler(a->handler, (int)delta, thishandled);
if (delta < nmi_longest_ns || delta < a->max_duration)continue;a->max_duration = delta;irq_work_queue(&a->irq_work);
nmi_check_duration(a, delta);rcu_read_unlock(); @@ -162,8 +162,6 @@ int __register_nmi_handler(unsigned int type, struct nmiaction *action) if (!action->handler) return -EINVAL;
- init_irq_work(&action->irq_work, nmi_max_handler);
- raw_spin_lock_irqsave(&desc->lock, flags);
/*