linux-kernel - Re: Re: [PATCH AUTOSEL 6.11 237/244] iomap: fix iomap_dio

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Message-ID: <xoxm6xlxqew2l3cbuahvkepcnckkiwa3ywetcyqep5hsq62mx5@xgmt3issrki6>
Date: Thu, 26 Sep 2024 09:58:24 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Dave Chinner <david@...morbit.com>
Cc: Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org, Pankaj Raghav <p.raghav@...sung.com>, 
	Hannes Reinecke <hare@...e.de>, "Darrick J . Wong" <djwong@...nel.org>, 
	Dave Chinner <dchinner@...hat.com>, Daniel Gomez <da.gomez@...sung.com>, 
	Christian Brauner <brauner@...nel.org>, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Re: [PATCH AUTOSEL 6.11 237/244] iomap: fix iomap_dio_zero() for
 fs bs > system page size

On Wed, Sep 25, 2024 at 11:01:46PM +1000, Dave Chinner wrote:
> On Wed, Sep 25, 2024 at 07:27:38AM -0400, Sasha Levin wrote:
> > From: Pankaj Raghav <p.raghav@...sung.com>
> > 
> > [ Upstream commit 10553a91652d995274da63fc317470f703765081 ]
> > 
> > iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> > < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> > size < page_size. This is true for most filesystems at the moment.
> > 
> > If the block size > page size, this will send the contents of the page
> > next to zero page(as len > PAGE_SIZE) to the underlying block device,
> > causing FS corruption.
> > 
> > iomap is a generic infrastructure and it should not make any assumptions
> > about the fs block size and the page size of the system.
> 
> Please drop this. It is for support of new functionality that was
> just merged and has no relevance to older kernels. It is not a bug
> fix.
> 

I did not have any fixes by tag for this reason. So please drop this commit
from the queue.

> And ....
> 
> > +
> > +	set_memory_ro((unsigned long)page_address(zero_page),
> > +		      1U << IOMAP_ZERO_PAGE_ORDER);
> 
> .... this will cause stable kernel regressions.
> 
> It was removed later in the merge because it is unnecessary and
> causes boot failures on (at least) some Power architectures.
> 
> -Dave.
> -- 
> Dave Chinner
> david@...morbit.com

-- 
Pankaj Raghav