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Date:   Thu, 7 Jul 2022 10:26:55 +0200
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Subject: Re: [PATCH 01/20] block, blk_filter: enable block device filters
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To:     Christoph Hellwig <hch@infradead.org>
CC:     "axboe@kernel.dk" <axboe@kernel.dk>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <1655135593-1900-1-git-send-email-sergei.shtepa@veeam.com>
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 <YsWHHcCfSVFklh4M@infradead.org>
From:   Sergei Shtepa <sergei.shtepa@veeam.com>
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Thank you, Christoph, for your attention to the patch.

I am preparing the next version of the patch. In it, I planned to
simplify the bdev_filer code.
I will make changes in it, in accordance with your comments, and
will add your code and check it on my test labs.

But I'm not sure if using the blk_mq_freeze_queue() is appropriate.
If I understood the code correctly, it is based on the expectation
that the counter q->q_usage_counter will decrease to zero.
To increase it, a blk_queue_enter() is used. And at the time of
calling the filter_bio() in the submit_bio_noacct(), this counter
has not yet been increased. I will double check this and try to
get rid of the bdev->bd_filter_lock.