linux-kernel - Re: [RFC v2 6/6] fs: add automatic kernel fs freeze / thaw and remove kthread freezing

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Message-ID: <Y7zJXRw2w6c0fFzY@bombadil.infradead.org>
Date:   Mon, 9 Jan 2023 18:11:41 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     rafael@...nel.org, gregkh@...uxfoundation.org,
        viro@...iv.linux.org.uk, jack@...e.cz, bvanassche@....org,
        jeyu@...nel.org, ebiederm@...ssion.com, mchehab@...nel.org,
        keescook@...omium.org, linux-fsdevel@...r.kernel.org,
        kernel@...force.de, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [RFC v2 6/6] fs: add automatic kernel fs freeze / thaw and
 remove kthread freezing

On Tue, Apr 20, 2021 at 06:47:03PM +0000, Luis Chamberlain wrote:
> On Tue, Apr 20, 2021 at 01:59:03PM +0100, Christoph Hellwig wrote:
> > > This also removes all the superflous freezer calls on all filesystems
> > > as they are no longer needed as the VFS now performs filesystem
> > > freezing/thaw if the filesystem has support for it. The filesystem
> > > therefore is in charge of properly dealing with quiescing of the
> > > filesystem through its callbacks.
> > 
> > Can you split that out from the main logic change?  Maybe even into one
> > patch per file system?
> 
> The issue with this is that once you do the changes in pm to
> freeze/suspend, if you leave the other changes in for the filesystems
> freeze / resume will stall, so all this needs to be an atomic operation
> if we want bisectable kernels.

So I'm thinking one way to split this up is to add an internal sb
flag for *if* a fs has support for this, and if so then we use the
generic fs freezer solution.

I'm not however too keen on the idea of mix and matching filesystems
on top of each other with different solutions, *but* if this makes it
easier for review / integration - it may be worth it. Let me know.

  Luis