linux-kernel - Re: [PATCH v2 09/10] block: panic if block debugfs dir is not created

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Date:   Mon, 20 Apr 2020 13:38:50 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     axboe@...nel.dk, viro@...iv.linux.org.uk, bvanassche@....org,
        rostedt@...dmis.org, mingo@...hat.com, jack@...e.cz,
        ming.lei@...hat.com, nstange@...e.de, akpm@...ux-foundation.org,
        mhocko@...e.com, yukuai3@...wei.com, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/10] block: panic if block debugfs dir is not created

On Sun, Apr 19, 2020 at 07:45:28PM +0000, Luis Chamberlain wrote:
> If DEBUG_FS is disabled we have another inline
> blk_debugfs_register() which just returns 0.
> 
> If BLK_DEV_IO_TRACE is enabled we rely on the block debugfs
> directory to have been created. If BLK_DEV_IO_TRACE is not enabled
> though, but if debugfs is still enabled we will always create a
> debugfs directory for a request_queue. Instead of special-casing
> this just for BLK_DEV_IO_TRACE, ensure this block debugfs dir is
> always created at boot if we have enabled debugfs.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  block/blk-debugfs.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/block/blk-debugfs.c b/block/blk-debugfs.c
> index 761318dcbf40..d6ec980e7531 100644
> --- a/block/blk-debugfs.c
> +++ b/block/blk-debugfs.c
> @@ -15,6 +15,8 @@ struct dentry *blk_debugfs_root;
>  void blk_debugfs_register(void)
>  {
>  	blk_debugfs_root = debugfs_create_dir("block", NULL);
> +	if (!blk_debugfs_root)
> +		panic("Failed to create block debugfs directory\n");

How rude, never crash the kernel for something so trivial as that.

Heck, never do ANYTHING different in the kernel if debugfs fails to do
something you think it should do.  This is debugging code, nothing
should ever depend on it, so just save the value (if you need it) and
move on.  Never check the value, as it means nothing to you.

greg k-h