linux-kernel - Re: [PATCH v2 5/6] super: use common iterator (Part 2)

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Message-ID: <20250331-klartext-lebst-d73d3ba0fca2@brauner>
Date: Mon, 31 Mar 2025 12:15:41 +0200
From: Christian Brauner <brauner@...nel.org>
To: Jan Kara <jack@...e.cz>
Cc: linux-fsdevel@...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 v2 5/6] super: use common iterator (Part 2)

On Mon, Mar 31, 2025 at 12:07:12PM +0200, Jan Kara wrote:
> On Sat 29-03-25 09:42:18, Christian Brauner wrote:
> > Use a common iterator for all callbacks. We could go for something even
> > more elaborate (advance step-by-step similar to iov_iter) but I really
> > don't think this is warranted.
> > 
> > Signed-off-by: Christian Brauner <brauner@...nel.org>
> 
> Looks good, one nit below. With that fixed feel free to add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>
> 
> > +#define invalid_super list_entry_is_head
> 
> Why do you have this invalid_super define? I find it rather confusing in
> the loop below and list_entry_is_head() would be much more
> understandable...

Fair, I just wanted a shorter name but I'll change it to
list_entry_is_head() and push it out.

> 
> 								Honza
> 
> > +
> > +static void __iterate_supers(void (*f)(struct super_block *, void *), void *arg,
> > +			     enum super_iter_flags_t flags)
> >  {
> >  	struct super_block *sb, *p = NULL;
> > +	bool excl = flags & SUPER_ITER_EXCL;
> >  
> > -	spin_lock(&sb_lock);
> > -	list_for_each_entry(sb, &super_blocks, s_list) {
> > -		bool locked;
> > +	guard(spinlock)(&sb_lock);
> >  
> > +	for (sb = first_super(flags); !invalid_super(sb, &super_blocks, s_list);
> > +	     sb = next_super(sb, flags)) {
> >  		if (super_flags(sb, SB_DYING))
> >  			continue;
> >  		sb->s_count++;
> >  		spin_unlock(&sb_lock);
> >  
> > -		locked = super_lock(sb, excl);
> > -		if (locked) {
> > +		if (flags & SUPER_ITER_UNLOCKED) {
> > +			f(sb, arg);
> > +		} else if (super_lock(sb, excl)) {
> >  			f(sb, arg);
> >  			super_unlock(sb, excl);
> >  		}
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR