linux-ext4 - Re: writeback completion soft lockup BUG in folio_wake

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Message-ID: <YkR9gu4Ye2uydkTd@infradead.org>
Date:   Wed, 30 Mar 2022 08:55:46 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>,
        Brian Foster <bfoster@...hat.com>,
        Linux-MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Namjae Jeon <namjae.jeon@...sung.com>,
        Ashish Sangwan <a.sangwan@...sung.com>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: writeback completion soft lockup BUG in folio_wake_bit()

On Sat, Mar 19, 2022 at 12:23:04PM -0400, Theodore Ts'o wrote:
> So the thing that I've been waiting to do for a while is to replace
> the whole data=ordered vs data=writeback and dioread_nolock and
> dioread_lock is a complete reworking of the ext4 buffered writeback
> path, where we write the data blocks *first*, and only then update the
> ext4 metadata.

> *) Determining where the new allocated data blockblocks should be, and
>    preventing those blocks from being used for any other purposes, but
>    *not* updating the file system metadata to reflect that change.
> 
> *) Submit the data block write
> 
> *) On write completion, update the metadata blocks in a kernel thread.

I think that would be easily done by switching to the iomap buffered
I/O code, which is very much built around that model.