From: Changbin Du <changbin.du@xxxxxxxxx> [ 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. [ bp: Massage. ] Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20200111125427.15662-1-changbin.du@xxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- arch/x86/include/asm/nmi.h | 1 - arch/x86/kernel/nmi.c | 20 +++++++++----------- 2 files changed, 9 insertions(+), 12 deletions(-) diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h index 75ded1d13d98d..9d5d949e662e1 100644 --- a/arch/x86/include/asm/nmi.h +++ b/arch/x86/include/asm/nmi.h @@ -41,7 +41,6 @@ struct nmiaction { struct list_head list; nmi_handler_t handler; u64 max_duration; - struct irq_work irq_work; unsigned long flags; const char *name; }; 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); /* -- 2.20.1
