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Date:   Wed, 9 Nov 2022 13:35:25 +0800
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Subject: Re: [Linux-cachefs] [PATCH v2 2/2] netfs: Fix dodgy maths
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To:     David Howells <dhowells@redhat.com>, willy@infradead.org
Cc:     linux-fsdevel@vger.kernel.org, linux-cachefs@redhat.com,
        Jeff Layton <jlayton@kernel.org>, linux-kernel@vger.kernel.org
References: <166757987929.950645.12595273010425381286.stgit@warthog.procyon.org.uk>
 <166757988611.950645.7626959069846893164.stgit@warthog.procyon.org.uk>
From:   JeffleXu <jefflexu@linux.alibaba.com>
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On 11/5/22 12:38 AM, David Howells wrote:
> Fix the dodgy maths in netfs_rreq_unlock_folios().  start_page could be
> inside the folio, in which case the calculation of pgpos will be come up
> with a negative number (though for the moment rreq->start is rounded down
> earlier and folios would have to get merged whilst locked)
> 
> Alter how this works to just frame the tracking in terms of absolute file
> positions, rather than offsets from the start of the I/O request.  This
> simplifies the maths and makes it easier to follow.
> 
> Fix the issue by using folio_pos() and folio_size() to calculate the end
> position of the page.
> 
> Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers")
> Reported-by: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Jeff Layton <jlayton@kernel.org>
> cc: linux-cachefs@redhat.com
> cc: linux-fsdevel@vger.kernel.org
> Link: https://lore.kernel.org/r/Y2SJw7w1IsIik3nb@casper.infradead.org/

Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>

-- 
Thanks,
Jingbo