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Date:   Fri, 28 Apr 2023 03:56:13 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Dave Chinner <dchinner@redhat.com>
Cc:     Ming Lei <ming.lei@redhat.com>, Theodore Ts'o <tytso@mit.edu>,
        linux-ext4@vger.kernel.org,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        linux-block@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        Eric Sandeen <sandeen@redhat.com>,
        Christoph Hellwig <hch@lst.de>, Zhang Yi <yi.zhang@redhat.com>
Subject: Re: [ext4 io hang] buffered write io hang in balance_dirty_pages
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On Fri, Apr 28, 2023 at 09:33:20AM +1000, Dave Chinner wrote:
> The block device needs to be shutting down the filesystem when it
> has some sort of fatal, unrecoverable error like this (e.g. hot
> unplug). We have the XFS_IOC_GOINGDOWN ioctl for telling the
> filesystem it can't function anymore. This ioctl
> (_IOR('X',125,__u32)) has also been replicated into ext4, f2fs and
> CIFS and it gets exercised heavily by fstests. Hence this isn't XFS
> specific functionality, nor is it untested functionality.
> 
> The ioctl should be lifted to the VFS as FS_IOC_SHUTDOWN and a
> super_operations method added to trigger a filesystem shutdown.
> That way the block device removal code could simply call
> sb->s_ops->shutdown(sb, REASON) if it exists rather than
> sync_filesystem(sb) if there's a superblock associated with the
> block device. Then all these 

I think this is the wrong approach.  Not that I've had any time to
work on my alternative approach:

https://www.infradead.org/~willy/banbury.html