linux-kernel - Re: [PATCH 1/6] ext4: replace kthread freezing with auto fs freezing

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Message-ID: <2nqlkokmbkvamnrza3fpjjmye3w3fy7gf5bqpjt2cxeviks5ax@u4wqm4ldxuy6>
Date: Tue, 1 Apr 2025 12:08:24 +0200
From: Jan Kara <jack@...e.cz>
To: Christian Brauner <brauner@...nel.org>
Cc: Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org, 
	Ard Biesheuvel <ardb@...nel.org>, linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	James Bottomley <James.Bottomley@...senpartnership.com>, mcgrof@...nel.org, 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: [PATCH 1/6] ext4: replace kthread freezing with auto fs freezing

On Tue 01-04-25 11:35:56, Christian Brauner wrote:
> On Tue, Apr 01, 2025 at 11:16:18AM +0200, Jan Kara wrote:
> > > ---
> > >  fs/ext4/mballoc.c | 2 +-
> > >  fs/ext4/super.c   | 3 ---
> > >  2 files changed, 1 insertion(+), 4 deletions(-)
> > > 
> > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > > index 0d523e9fb3d5..ae235ec5ff3a 100644
> > > --- a/fs/ext4/mballoc.c
> > > +++ b/fs/ext4/mballoc.c
> > > @@ -6782,7 +6782,7 @@ static ext4_grpblk_t ext4_last_grp_cluster(struct super_block *sb,
> > >  
> > >  static bool ext4_trim_interrupted(void)
> > >  {
> > > -	return fatal_signal_pending(current) || freezing(current);
> > > +	return fatal_signal_pending(current);
> > >  }
> > 
> > This change should not happen. ext4_trim_interrupted() makes sure FITRIM
> > ioctl doesn't cause hibernation failures and has nothing to do with kthread
> > freezing...
> > 
> > Otherwise the patch looks good.
> 
> Afaict, we don't have to do these changes now. Yes, once fsfreeze
> reliably works in the suspend/resume codepaths then we can switch all
> that off and remove the old freezer. But we should only do that once we
> have some experience with the new filesystem freezing during
> suspend/hibernate. So we should place this under a
> /sys/power/freeze_filesystems knob and wait a few kernel releases to see
> whether we see significant problems. How does that sound to you?

I agree that enabling this with some knob to allow easy way out if things
don't work makes sense. And the removal of kthread freezing can be done
somewhat later when we are more confident filesystem freezing on
hibernation is solid.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR