Re: [RFC PATCH 00/11] printk: safe printing in NMI context

[Jiri Kosina]

On Fri, 9 May 2014, Petr Mladek wrote:

> printk() cannot be used safely in NMI context because it uses internal locks
> and thus could cause a deadlock. Unfortunately there are circumstances when
> calling printk from NMI is very useful. For example, all WARN.*(in_nmi())
> would be much more helpful if they didn't lockup the machine.
> 
> Another example would be arch_trigger_all_cpu_backtrace for x86 which uses NMI
> to dump traces on all CPU (either triggered by sysrq+l or from RCU stall
> detector).

I am rather surprised that this patchset hasn't received a single review 
comment for 3 weeks.

Let me point out that the issues Petr is talking about in the cover letter 
are real -- we've actually seen the lockups triggered by RCU stall 
detector trying to dump stacks on all CPUs, and hard-locking machine up 
while doing so.

So this really needs to be solved.

-- 
Jiri Kosina
SUSE Labs
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