Re: [PATCH 5/7 V2] workqueue: reuse the current default pwq when its attrs unchanged

[Tejun Heo]

Hello,

On Tue, May 12, 2015 at 08:32:33PM +0800, Lai Jiangshan wrote:
> When apply_wqattrs_prepare() is called, it is possible that the default
> pwq is unaffected.  It is always true that only the NUMA affinity is being
> changed and sometimes true that the low level cpumask is being changed.
> 
> So we try to reuse the current default pwq when its attrs unchanged.
> 
> After this change, "ctx->dfl_pwq->refcnt++" could be dangerous
> when ctx->dfl_pwq is being reused, so we use get_pwq_unlocked() instead.

Can you elaborate the above paragraph?  Why wouldn't that be dangerous
before this change?

Thanks.

-- 
tejun
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