linux-kernel - Re: [RFC PATCH 4/4] vfs: add filesystem freeze/thaw callbacks for power management

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Message-ID: <6cd9f94e5c80883534fad561123e0ce3d1837599.camel@HansenPartnership.com>
Date: Fri, 28 Mar 2025 10:40:26 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
 mcgrof@...nel.org, jack@...e.cz, hch@...radead.org, david@...morbit.com, 
 rafael@...nel.org, djwong@...nel.org, pavel@...nel.org,
 peterz@...radead.org,  mingo@...hat.com, will@...nel.org,
 boqun.feng@...il.com
Subject: Re: [RFC PATCH 4/4] vfs: add filesystem freeze/thaw callbacks for
 power management

On Fri, 2025-03-28 at 13:01 +0100, Christian Brauner wrote:
> On Thu, Mar 27, 2025 at 10:06:13AM -0400, James Bottomley wrote:
[...]
> > diff --git a/fs/super.c b/fs/super.c
> > index 76785509d906..b4b0986414b0 100644
> > --- a/fs/super.c
> > +++ b/fs/super.c
> > @@ -1461,6 +1461,67 @@ static struct super_block
> > *get_bdev_super(struct block_device *bdev)
> >  	return sb;
> >  }
> >  
> > +/*
> > + * Kernel freezing and thawing is only done in the power
> > management
> > + * subsystem and is thus single threaded (so we don't have to
> > worry
> > + * here about multiple calls to filesystems_freeze/thaw().
> > + */
> > +
> > +static int freeze_flags;
> > +
> > +static void filesystems_freeze_callback(struct super_block *sb)
> > +{
> > +	/* errors don't fail suspend so ignore them */
> > +	if (sb->s_op->freeze_super)
> > +		sb->s_op->freeze_super(sb, FREEZE_MAY_NEST
> > +				       | FREEZE_HOLDER_KERNEL
> > +				       | freeze_flags);
> > +	else if (sb->s_bdev)
> > +		freeze_super(sb, FREEZE_MAY_NEST |
> > FREEZE_HOLDER_KERNEL
> > +			     | freeze_flags);
> > +	else {
> > +		pr_info("Ignoring filesystem %s\n", sb->s_type-
> > >name);
> > +		return;
> > +	}
> > +
> > +	pr_info("frozen %s, now syncing block ...", sb->s_type-
> > >name);
> > +	sync_blockdev(sb->s_bdev);
> 
> Unnecessary, either the filesystem is responsible for this if it
> provides its own ->freeze_super() or freeze_super() does it in
> sync_filesystem.

I simply copied it from super.c:fs_bdev_freeze(), so is the
sync_blockdev() in there unnecessary as well?

Regards,

James