I hit a pr_warn() inside hrtimer_interrupt() which lead to a BUG: Invalid wait context splat.
The problem wasn't reproducible but I think the cause is obvious, printk can't be called from interrupt context. AFAICU printk_deferred() is safe from NMI, so I assumed it is safe to be called from hrtimer_interrupt() too. Adding a pr_warn_once() inside hrtimer_interrupt() in a location where it is always hit produces the BUG splat. Replacing it with pr_warn_deferred_once() generates the printk warning without any splat. I added a new pr_*_deferred_once() variants to avoid open coding; but the name ended not much shorter and I'm not sure if the wrappers are a win overall. Since I've already done it, I'm sticking to it in this post. But will be happy to drop it and just open code the printk_deferred_once(KERN_WARN, ...) in hrtimer_interrupt() instead. Thanks Qais Yousef (2): printk: Add new pr_*_deferred_once() variants hrtimer: Use pr_warn_deferred_once() in hrtimer_interrupt() include/linux/printk.h | 24 ++++++++++++++++++++++++ kernel/time/hrtimer.c | 3 ++- 2 files changed, 26 insertions(+), 1 deletion(-) -- 2.25.1
