linux-kernel - Re: [PATCH 1/6] fs: unify locking semantics for fs freeze / thaw

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Message-ID: <ZIFgmjywefaAqLGi@infradead.org>
Date:   Wed, 7 Jun 2023 22:01:14 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     hch@...radead.org, djwong@...nel.org, sandeen@...deen.net,
        song@...nel.org, rafael@...nel.org, gregkh@...uxfoundation.org,
        viro@...iv.linux.org.uk, jack@...e.cz, jikos@...nel.org,
        bvanassche@....org, ebiederm@...ssion.com, mchehab@...nel.org,
        keescook@...omium.org, p.raghav@...sung.com, da.gomez@...sung.com,
        linux-fsdevel@...r.kernel.org, kernel@...force.de,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] fs: unify locking semantics for fs freeze / thaw

On Sun, May 07, 2023 at 06:17:12PM -0700, Luis Chamberlain wrote:
> Right now freeze_super()  and thaw_super() are called with
> different locking contexts. To expand on this is messy, so
> just unify the requirement to require grabbing an active
> reference and keep the superblock locked.
> 
> Suggested-by: Christoph Hellwig <hch@...radead.org>
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>

Maybe I'm just getting old, but where did I suggest this?

That being said, holding an active reference over any operation is a
good thing.  As Jan said it can be done way simpler than this, though.

Also please explain the actual different locking contexts and what
semantics you unify in the commit log please.

> - * freeze_super - lock the filesystem and force it into a consistent state
> + * freeze_super - force a filesystem backed by a block device into a consistent state
>   * @sb: the super to lock

This is not actually true.  Nothing in here has anything to do
with block devices, and it is used on a at least one non-block file
system.