linux-kernel - Re: [PATCH 02/17] nilfs2: eliminate staggered calls to kunmap in nilfs

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Message-ID: <ZWTNKhFukc+ZxRJA@casper.infradead.org>
Date:   Mon, 27 Nov 2023 17:08:58 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Ryusuke Konishi <konishi.ryusuke@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-nilfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/17] nilfs2: eliminate staggered calls to kunmap in
 nilfs_rename

On Mon, Nov 27, 2023 at 11:30:21PM +0900, Ryusuke Konishi wrote:
> In nilfs_rename(), calls to nilfs_put_page() to release pages obtained
> with nilfs_find_entry() or nilfs_dotdot() are alternated in the normal
> path.
> 
> When replacing the kernel memory mapping method from kmap to
> kmap_local_{page,folio}, this violates the constraint on the calling
> order of kunmap_local().
> 
> Swap the order of nilfs_put_page calls where the kmap sections of
> multiple pages overlap so that they are nested, allowing direct
> replacement of nilfs_put_page() -> unmap_and_put_page().
> 
> Without this reordering, that replacement will cause a kernel WARNING
> in kunmap_local_indexed() on architectures with high memory mapping.
> 
> Signed-off-by: Ryusuke Konishi <konishi.ryusuke@...il.com>
> Cc: Matthew Wilcox (Oracle) <willy@...radead.org>

Thanks for catching this!

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>