linux-kernel - Re: [PATCH RT] nvdimm: make lane acquirement RT aware

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Message-ID: <CAPcyv4h7a8QSvJiUqCd=r3KPaWwiPC_-9x3Jip6eY2XGJ5Wc0w@mail.gmail.com>
Date:   Wed, 6 Mar 2019 08:35:21 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Yongxin Liu <yongxin.liu@...driver.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-rt-users@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Pankaj Gupta <pagupta@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH RT] nvdimm: make lane acquirement RT aware

On Wed, Mar 6, 2019 at 2:05 AM Yongxin Liu <yongxin.liu@...driver.com> wrote:
>
> Currently, nvdimm driver isn't RT compatible.
> nd_region_acquire_lane() disables preemption with get_cpu() which
> causes "scheduling while atomic" spews on RT, when using fio to test
> pmem as block device.
>
> In this change, we replace get_cpu/put_cpu with local_lock_cpu/
> local_unlock_cpu, and introduce per CPU variable "ndl_local_lock".
> Due to preemption on RT, this lock can avoid race condition for the
> same lane on the same CPU. When CPU number is greater than the lane
> number, lane can be shared among CPUs. "ndl_lock->lock" is used to
> protect the lane in this situation.
>
> This patch is derived from Dan Williams and Pankaj Gupta's proposal from
> https://www.mail-archive.com/linux-nvdimm@lists.01.org/msg13359.html
> and https://www.spinics.net/lists/linux-rt-users/msg20280.html.
> Many thanks to them.
>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Pankaj Gupta <pagupta@...hat.com>
> Cc: linux-rt-users <linux-rt-users@...r.kernel.org>
> Cc: linux-nvdimm <linux-nvdimm@...ts.01.org>
> Signed-off-by: Yongxin Liu <yongxin.liu@...driver.com>

Looks ok to me in concept.

Acked-by: Dan Williams <dan.j.williams@...el.com>