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

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Message-ID: <ZwHaHrQNr1KbgyN3@sashalap>
Date: Sat, 5 Oct 2024 20:30:22 -0400
From: Sasha Levin <sashal@...nel.org>
To: Dave Chinner <david@...morbit.com>
Cc: 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: [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.
>
>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.

Dropped, and sorry about sending this one out twice!

-- 
Thanks,
Sasha