linux-kernel - Re: [PATCH V14 04/24] mmc: block: Ensure that debugfs files are removed

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Date:   Thu, 23 Nov 2017 14:22:34 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Bough Chen <haibo.chen@....com>,
        Alex Lemberg <alex.lemberg@...disk.com>,
        Mateusz Nowak <mateusz.nowak@...el.com>,
        Yuliy Izrailov <Yuliy.Izrailov@...disk.com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Dong Aisheng <dongas86@...il.com>,
        Das Asutosh <asutoshd@...eaurora.org>,
        Zhangfei Gao <zhangfei.gao@...il.com>,
        Sahitya Tummala <stummala@...eaurora.org>,
        Harjani Ritesh <riteshh@...eaurora.org>,
        Venu Byravarasu <vbyravarasu@...dia.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V14 04/24] mmc: block: Ensure that debugfs files are removed

On Tue, Nov 21, 2017 at 2:42 PM, Adrian Hunter <adrian.hunter@...el.com> wrote:

> The card is not necessarily being removed, but the debugfs files must be
> removed when the driver is removed, otherwise they will continue to exist
> after unbinding the card from the driver. e.g.
>
>   # echo "mmc1:0001" > /sys/bus/mmc/drivers/mmcblk/unbind
>   # cat /sys/kernel/debug/mmc1/mmc1\:0001/ext_csd
>   [  173.634584] BUG: unable to handle kernel NULL pointer dereference at 0000000000000050
>   [  173.643356] IP: mmc_ext_csd_open+0x5e/0x170
>
> A complication is that the debugfs_root may have already been removed, so
> check for that too.
>
> Fixes: 627c3ccfb46a ("mmc: debugfs: Move block debugfs into block module")
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

I was assuming debugfs would always be removed from debugfs.c
using debugfs_remove_recursive(card->debugfs_root) but that
doesn't work for this case where we bin/unbind the block layer
interactively, sorry for missing it :(

Ulf: I think this can go in as an *early* fix as well, say after -rc1.

Yours,
Linus Walleij