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Date: Wed, 27 May 2015 16:14:23 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Petr Mladek <pmladek@...e.cz> Cc: Frederic Weisbecker <fweisbec@...il.com>, Steven Rostedt <rostedt@...dmis.org>, Dave Anderson <anderson@...hat.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Kay Sievers <kay@...y.org>, Jiri Kosina <jkosina@...e.cz>, Michal Hocko <mhocko@...e.cz>, Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org, Wang Long <long.wanglong@...wei.com>, peifeiyue@...wei.com, dzickus@...hat.com, morgan.wang@...wei.com, sasha.levin@...cle.com Subject: Re: [PATCH 04/10] printk: Merge and flush NMI buffer predictably via IRQ work On Mon, 25 May 2015 14:46:27 +0200 Petr Mladek <pmladek@...e.cz> wrote: > It might take ages until users see messages from NMI context. They cannot > be flushed to the console because the operation involves taking and > releasing a bunch of locks. Everything gets fixed by the followup printk > in normal context but it is not predictable. > > The same problem has printk_sched() and this patch reuses the existing > solution. > > There is no special printk() variant for NMI context. Hence the IRQ work > need to get queued from vprintk_emit(). > > ... > > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -1554,9 +1554,6 @@ int printk_deferred(const char *fmt, ...) > va_start(args, fmt); > r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args); > va_end(args); > - > - __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT); > - irq_work_queue(this_cpu_ptr(&wake_up_klogd_work)); > preempt_enable(); > > return r; > @@ -1880,7 +1877,10 @@ asmlinkage int vprintk_emit(int facility, int level, > * If called from the scheduler or NMI context, we can not get console > * without a possible deadlock. > */ > - if (!in_sched && !in_nmi()) { > + if (in_sched || in_nmi()) { > + __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT); > + irq_work_queue(this_cpu_ptr(&wake_up_klogd_work)); > + } else { This looks hairy. Why irq_work_queue() OK to call from NMI? arch/arm64/kernel/smp.c uses smp_cross_call() which might use NMI! Presumably it'll call directly if the target CPU==this_cpu but I didn't run around and audit everything. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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