Re: [PATCH 0/4] Convert timekeeping core to use printk_deferred (v2)

[John Stultz]

On 05/02/2014 04:05 PM, Andrew Morton wrote:
> On Fri,  2 May 2014 15:09:14 -0700 John Stultz <john.stultz@xxxxxxxxxx> wrote:
>
>> Recently, Jiri pointed out a potential deadlock when calling printk
>> while holding the timekeeping seqlock.
>>
>> Annoyingly, the seqlock lockdep enablement doesn't catch this, as
>> printk disables lockdep.
>>
>> When looking for possible solutions, one idea was to use a local buffer
>> and defer the printk to later. Ends up there is already similar
>> functionality in printk_sched() to avoid similar style deadlocks w/
>> the scheduler.
>>
>> Thus this patchset (based on next/akpm) renames printk_sched to
>> printk_deferred and then moves the affected timekeeping printks to make
>> use of it.
>>
>> There were some points in the discussion between Jan and Peter that
>> made it seem that there may still be problems lurking in the console
>> layer, and I'm not sure I fully understand their point, so this solution
>> may be incomplete.
>>
>> Additionally, the same issue likely affects any WARN_ONs as well, but
>> I wanted to get some thoughts on this approach before trying to remove
>> or convert affected WARN_ONS.
>>
>> Your thoughts and feedback are greatly appreciated!
> All look pretty simple and sane to me.  printk is a crazy hotspot
> lately but this patchset looks like it won't get singed.
>
> Would "printk_deferred_once" be more logical than
> "printk_once_deferred"?  Think so.  It's (((printk(deferred(once))),
> not (((printk(once(deferred))).

Sounds good.  Will update the set with this.

thanks!
-john

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