linux-kernel - Re: [PATCH 1/4] iomap: make sure iomap_adjust_read_range() are aligned with block

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Message-ID: <20250915091207.4094376-1-alexjlzheng@tencent.com>
Date: Mon, 15 Sep 2025 17:12:07 +0800
From: Jinliang Zheng <alexjlzheng@...il.com>
To: kernel@...kajraghav.com
Cc: alexjlzheng@...il.com,
	alexjlzheng@...cent.com,
	brauner@...nel.org,
	djwong@...nel.org,
	hch@...radead.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-xfs@...r.kernel.org,
	yi.zhang@...wei.com
Subject: Re: [PATCH 1/4] iomap: make sure iomap_adjust_read_range() are aligned with block_size

On Mon, 15 Sep 2025 10:54:00 +0200, kernel@...kajraghav.com wrote:
> On Sun, Sep 14, 2025 at 08:40:06PM +0800, Jinliang Zheng wrote:
> > On Sun, 14 Sep 2025 13:45:16 +0200, kernel@...kajraghav.com wrote:
> > > On Sat, Sep 14, 2025 at 11:37:15AM +0800, alexjlzheng@...il.com wrote:
> > > > From: Jinliang Zheng <alexjlzheng@...cent.com>
> > > > 
> > > > iomap_folio_state marks the uptodate state in units of block_size, so
> > > > it is better to check that pos and length are aligned with block_size.
> > > > 
> > > > Signed-off-by: Jinliang Zheng <alexjlzheng@...cent.com>
> > > > ---
> > > >  fs/iomap/buffered-io.c | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > > > 
> > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > > > index fd827398afd2..0c38333933c6 100644
> > > > --- a/fs/iomap/buffered-io.c
> > > > +++ b/fs/iomap/buffered-io.c
> > > > @@ -234,6 +234,9 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
> > > >  	unsigned first = poff >> block_bits;
> > > >  	unsigned last = (poff + plen - 1) >> block_bits;
> > > >  
> > > > +	WARN_ON(*pos & (block_size - 1));
> > > > +	WARN_ON(length & (block_size - 1));
> > > Any reason you chose WARN_ON instead of WARN_ON_ONCE?
> > 
> > I just think it's a fatal error that deserves attention every time
> > it's triggered.
> > 
> 
> Is this a general change or does your later changes depend on these on
> warning to work correctly?

No, there is no functional change.

I added it only because the correctness of iomap_adjust_read_range() depends on
it, so it's better to hightlight it now.

```
	/* move forward for each leading block marked uptodate */
	for (i = first; i <= last; i++) {
		if (!ifs_block_is_uptodate(ifs, i))
			break;
		*pos += block_size; <-------------------- if not aligned, ...
		poff += block_size;
		plen -= block_size;
		first++;
	}
```

> 
> > > 
> > > I don't see WARN_ON being used in iomap/buffered-io.c.
> > 
> > I'm not sure if there are any community guidelines for using these
> > two macros. If there are, please let me know and I'll be happy to
> > follow them as a guide.
> 
> We typically use WARN_ON_ONCE to prevent spamming.

If you think it's better, I will send a new version.

thanks,
Jinliang Zheng. :)

> 
> --
> Pankaj