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Date:   Thu, 27 Jan 2022 10:49:42 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Jan Kara <jack@suse.cz>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-block@vger.kernel.org, Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH 3/8] block: remove the racy
 bd_inode->i_mapping->nrpages asserts
Message-ID: <20220127094942.GA14727@lst.de>
References: <20220126155040.1190842-1-hch@lst.de> <20220126155040.1190842-4-hch@lst.de> <20220127094737.dosrg7xbnwuw3ttx@quack3.lan>
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On Thu, Jan 27, 2022 at 10:47:37AM +0100, Jan Kara wrote:
> On Wed 26-01-22 16:50:35, Christoph Hellwig wrote:
> > Nothing prevents a file system or userspace opener of the block device
> > from redirtying the page right afte sync_blockdev returned.  Fortunately
> > data in the page cache during a block device change is mostly harmless
> > anyway.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> My understanding was these warnings are there to tell userspace it is doing
> something wrong. Something like the warning we issue when DIO races with
> buffered IO... I'm not sure how useful they are but I don't see strong
> reason to remove them either...

Well, it is not just a warning, but also fails the command.  With some of
the reduced synchronization blktests loop/002 can hit them pretty reliably.