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

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Message-ID: <20200210023240.GA10029@ming.t460p>
Date:   Mon, 10 Feb 2020 10:32:40 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     "yukuai (C)" <yukuai3@...wei.com>
Cc:     Bart Van Assche <bvanassche@....org>, axboe@...nel.dk,
        chaitanya.kulkarni@....com, damien.lemoal@....com,
        dhowells@...hat.com, asml.silence@...il.com, ajay.joshi@....com,
        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 Mon, Feb 10, 2020 at 10:13:22AM +0800, yukuai (C) wrote:
> On 2020/2/10 9:00, Bart Van Assche wrote:
> > Have you already noticed patch "[PATCH] blktrace: Protect q->blk_trace
> > with RCU"? If not, have you already tried to verify whether that patch
> > fixes the use-after-free detected by syzbot?
> 
> I just tested and confirmed the patch didn't fix the problem.

Right, the two are for fixing different issue.

> 
> By the way, I think Ming is right about "So release not by wq just
> reduces the chance, instead of fixing it completely.", and "move
> blk_mq_debugfs_unregister() into blk_unregister_queue()" is a good
> choice. However, blk_trace_shutdown() and blk_mq_exit_queue() also
> remove some files or dirs, and they may need to move to
> blk_unregister_queue().

Right.

Fortunately, we hold sysfs_dir_lock in blk_unregister_queue(), so
the issue can be fixed by check & remove with holding the same lock
in blk_trace_free().


Thanks, 
Ming