Re: [RFC-v2 2/2] mmc: sdhci-msm: Add support for bus bandwidth voting

From: Doug Anderson <dianders@chromium.org>
To: Pradeep P V K <ppvk@codeaurora.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>,
	Georgi Djakov <georgi.djakov@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Asutosh Das <asutoshd@codeaurora.org>,
	Veerabhadrarao Badiganti <vbadigan@codeaurora.org>,
	Sahitya Tummala <stummala@codeaurora.org>,
	Sayali Lokhande <sayalil@codeaurora.org>,
	Ram Prakash Gupta <rampraka@codeaurora.org>,
	Stephen Boyd <sboyd@kernel.org>,
	Linux MMC List <linux-mmc@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>, Andy Gross <agross@kernel.org>,
	linux-mmc-owner@vger.kernel.org,
	Subhash Jadavani <subhashj@codeaurora.org>
Subject: Re: [RFC-v2 2/2] mmc: sdhci-msm: Add support for bus bandwidth voting
Date: Fri, 3 Apr 2020 10:04:23 -0700	[thread overview]
Message-ID: <CAD=FV=WGUasS=UZxFeSS0Cg=9WxHPMWVFyYae7CFmOxV2_yhJw@mail.gmail.com> (raw)
In-Reply-To: <1573220319-4287-3-git-send-email-ppvk@codeaurora.org>

Hi,

On Fri, Nov 8, 2019 at 5:45 AM Pradeep P V K <ppvk@codeaurora.org> wrote:
>
> +       if (msm_host->bus_vote_data->curr_vote != VOTE_ZERO)
> +               queue_delayed_work(system_wq,
> +                                  &msm_host->bus_vote_work,
> +                                  msecs_to_jiffies(MSM_MMC_BUS_VOTING_DELAY));
> +}

Drive-by feedback here without any full review of your patch...
Someone had your patch applied and sent me a stack trace with a
warning on it.  That warning showed:

workqueue: WQ_MEM_RECLAIM kblockd:blk_mq_run_work_fn is flushing
!WQ_MEM_RECLAIM events:sdhci_msm_bus_work

The trace shown was:

    check_flush_dependency+0x108/0x110
    __flush_work+0xa8/0x1e8
    __cancel_work_timer+0x130/0x1c4
    cancel_delayed_work_sync+0x20/0x30
    sdhci_msm_bus_cancel_work_and_set_vote+0x3c/0x8c
    sdhci_msm_bus_voting+0x40/0x7c
    sdhci_msm_runtime_resume+0xdc/0xf4
    pm_generic_runtime_resume+0x34/0x48
    __rpm_callback+0x70/0xfc
    rpm_callback+0x5c/0x8c
    rpm_resume+0x3fc/0x534
    __pm_runtime_resume+0x7c/0xa0
    __mmc_claim_host+0x1f4/0x230
    mmc_get_card+0x34/0x40
    mmc_mq_queue_rq+0x18c/0x244
    blk_mq_dispatch_rq_list+0x27c/0x560
    blk_mq_do_dispatch_sched+0xe0/0x140
    blk_mq_sched_dispatch_requests+0x138/0x1b8
    __blk_mq_run_hw_queue+0xc0/0x118
    blk_mq_run_work_fn+0x24/0x30

I believe the way to interpret this is that you need to be running
your work on a workqueue marked for memory reclaim.  That means you
can't use the system_wq to queue your work.  Without being an expert,
a quick guess would be that you should be queueing your work on the
"kblockd_workqueue" using one of the functions for this.

-Doug