linux-kernel - Re: [PATCH v2] md/bitmap: Avoid protection error writing bitmap page with block integrity

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Message-ID: <ZMdiEavzzRwAFjPq@infradead.org>
Date:   Mon, 31 Jul 2023 00:26:09 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jinyoung Choi <j-young.choi@...sung.com>
Cc:     "song@...nel.org" <song@...nel.org>,
        "linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pmenzel@...gen.mpg.de" <pmenzel@...gen.mpg.de>
Subject: Re: [PATCH v2] md/bitmap: Avoid protection error writing bitmap page
 with block integrity

On Thu, Jul 20, 2023 at 06:29:57PM +0900, Jinyoung Choi wrote:
> Changing the bitmap page is also possible on the page where the DMA is
> being performed or scheduled in the MD.

Are you guys actually using the whacky bitmap feature?  If so, this
really is the least of our problems and you need to invest some real
work into it to get it off ->bmap and into using ->read_iter and
->write_iter.  Right now Song has a series from me queued up to
deprecated it.

I also don't think a simple wait for existing writers prevents you
from other modifications, but maybe I'm issing something.