linux-kernel - Re: [PATCH] block: revert pushing the final release of request

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Date:   Mon, 10 Feb 2020 16:49:48 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Bart Van Assche <bvanassche@....org>, <axboe@...nel.dk>,
        <ming.lei@...hat.com>, <chaitanya.kulkarni@....com>,
        <damien.lemoal@....com>, <dhowells@...hat.com>,
        <asml.silence@...il.com>, <ajay.joshi@....com>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>, <zhangxiaoxu5@...wei.com>,
        <luoshijie1@...wei.com>, jan kara <jack@...e.cz>
Subject: Re: [PATCH] block: revert pushing the final release of request_queue
 to a workqueue.

On 2020/2/10 11:14, Bart Van Assche wrote:
> I think that calling blk_mq_exit_queue() from blk_unregister_queue()
> would break at least the sd driver. The sd driver can issue I/O after
> having called del_gendisk(). See also the sd_sync_cache() call in
> sd_shutdown().

If blk_mq_exit_queue() can't move to blk_unregister_queue(),
neither can blk_mq_debugfs_unregister(). It'a dead end.

The purpose is that when __blk_trace_setup() is called, the cleanup of
last loop_device(__blk_release_queue()) should finish aready.

I wonder if we can test that if the dir still exist in loop_add():

static int loop_add(struct loop_device **l, int i)
{
...
           char disk_name[DISK_NAME_LEN];
           struct dentry *dir, *root;

           sprintf(disk_name, "loop%d", i);
           root = debugfs_lookup("block", NULL);
           if (root) {
                   dir = debugfs_lookup(disk_name, root);
                   if (dir) {
                           dput(dir);
                           dput(root);
                          pr_err("Directory '%s' with parent 'block' 
already present!\n",disk_name);
                           return -EBUSY;
                   }
                   dput(root);
           }
...

Thanks!
Yu Kuai