linux-kernel - Re: [PATCH] percpu-refcount: relax limit on percpu_ref

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Date:   Sun, 09 Sep 2018 11:46:20 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Ming Lei <ming.lei@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Tejun Heo <tj@...nel.org>,
        Jianchao Wang <jianchao.w.wang@...cle.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        linux-block@...r.kernel.org
Subject: Re: [PATCH] percpu-refcount: relax limit on percpu_ref_reinit()

On Sun, 2018-09-09 at 20:58 +0800, Ming Lei wrote:
> Now percpu_ref_reinit() can only be done on one percpu refcounter
> when it drops zero. And the limit shouldn't be so strict, and it
> is quite straightforward that percpu_ref_reinit() can be done when
> this counter is at atomic mode.
> 
> This patch relaxes the limit, so we may avoid extra change[1] for NVMe
> timeout's requirement.
> 
> [1] https://marc.info/?l=linux-kernel&m=153612052611020&w=2

Is the NVMe driver the only block driver that hangs if it is attempted to
freeze its request queue when a request times out? If so, can this hang be
fixed by modifying the NVMe driver instead of by modifying the percpu
refcount implementation?

Thanks,

Bart.