linux-kernel - Re: [RFC v2 2/5] blktrace: fix debugfs use after free

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Message-ID: <88f94070-cd34-7435-9175-e0518a7d7db8@acm.org>
Date:   Thu, 9 Apr 2020 19:52:59 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Luis Chamberlain <mcgrof@...nel.org>, axboe@...nel.dk,
        viro@...iv.linux.org.uk, gregkh@...uxfoundation.org,
        rostedt@...dmis.org, mingo@...hat.com, jack@...e.cz,
        ming.lei@...hat.com, nstange@...e.de, akpm@...ux-foundation.org
Cc:     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, Omar Sandoval <osandov@...com>,
        Hannes Reinecke <hare@...e.com>,
        Michal Hocko <mhocko@...nel.org>,
        syzbot+603294af2d01acfdd6da@...kaller.appspotmail.com
Subject: Re: [RFC v2 2/5] blktrace: fix debugfs use after free

On 2020-04-09 14:45, Luis Chamberlain wrote:
> +void blk_q_debugfs_register(struct request_queue *q)
> +{
> +	q->debugfs_dir = debugfs_create_dir(kobject_name(q->kobj.parent),
> +					    blk_debugfs_root);
> +}
> +
> +void blk_q_debugfs_unregister(struct request_queue *q)
> +{
> +	debugfs_remove_recursive(q->debugfs_dir);
> +	q->debugfs_dir = NULL;
> +}

There are no other functions in the block layer that start with the
prefix blk_q_. How about changing that prefix into blk_?

> -#ifdef CONFIG_BLK_DEBUG_FS
> +#ifdef CONFIG_DEBUG_FS
>  	struct dentry		*debugfs_dir;
> +#endif

Please add a comment above 'debugfs_dir' that it is used not only by the
code in block/blk-*debugfs.c but also by the code in
kernel/trace/blktrace.c. Otherwise this patch looks good to me.

Thanks,

Bart.