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Date: Mon, 25 Mar 2024 19:15:59 +0000
From: Matthew Wilcox <willy@infradead.org>
To: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	gost.dev@samsung.com, chandan.babu@oracle.com, hare@suse.de,
	mcgrof@kernel.org, djwong@kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, david@fromorbit.com,
	akpm@linux-foundation.org, Pankaj Raghav <p.raghav@samsung.com>
Subject: Re: [PATCH v3 10/11] xfs: make the calculation generic in
 xfs_sb_validate_fsb_count()
Message-ID: <ZgHNb3Led05RXRd2@casper.infradead.org>
References: <20240313170253.2324812-1-kernel@pankajraghav.com>
 <20240313170253.2324812-11-kernel@pankajraghav.com>
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In-Reply-To: <20240313170253.2324812-11-kernel@pankajraghav.com>

On Wed, Mar 13, 2024 at 06:02:52PM +0100, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
> 
> Instead of assuming that PAGE_SHIFT is always higher than the blocklog,
> make the calculation generic so that page cache count can be calculated
> correctly for LBS.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>  fs/xfs/xfs_mount.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index aabb25dc3efa..9cf800586da7 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -133,9 +133,16 @@ xfs_sb_validate_fsb_count(
>  {
>  	ASSERT(PAGE_SHIFT >= sbp->sb_blocklog);

but ... you're still asserting that PAGE_SHIFT is larger than blocklog.
Shouldn't you delete that assertion?

>  	ASSERT(sbp->sb_blocklog >= BBSHIFT);
> +	uint64_t max_index;
> +	uint64_t max_bytes;
> +
> +	if (check_shl_overflow(nblocks, sbp->sb_blocklog, &max_bytes))
> +		return -EFBIG;
>  
>  	/* Limited by ULONG_MAX of page cache index */
> -	if (nblocks >> (PAGE_SHIFT - sbp->sb_blocklog) > ULONG_MAX)
> +	max_index = max_bytes >> PAGE_SHIFT;
> +
> +	if (max_index > ULONG_MAX)
>  		return -EFBIG;

This kind of depends on the implementation details of the page cache.
We have MAX_LFS_FILESIZE to abstract that; maybe that should be used
here?