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Date:   Mon, 6 Aug 2018 12:22:03 +0200
From:   Jan Kara <jack@suse.cz>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Jan Kara <jack@suse.cz>, Chengguang Xu <cgxu519@gmx.com>,
        mgorman@techsingularity.net, jlayton@redhat.com,
        ak@linux.intel.com, mawilcox@microsoft.com,
        tim.c.chen@linux.intel.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH] mm: adjust max read count in generic_file_buffered_read()
Message-ID: <20180806102203.hmobd26cujmlfcsw@quack2.suse.cz>
References: <20180719081726.3341-1-cgxu519@gmx.com>
 <20180719085812.sjup2odrjyuigt3l@quack2.suse.cz>
 <20180720161429.d63dccb9f66799dc0ff74dba@linux-foundation.org>
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On Fri 20-07-18 16:14:29, Andrew Morton wrote:
> On Thu, 19 Jul 2018 10:58:12 +0200 Jan Kara <jack@suse.cz> wrote:
> 
> > On Thu 19-07-18 16:17:26, Chengguang Xu wrote:
> > > When we try to truncate read count in generic_file_buffered_read(),
> > > should deliver (sb->s_maxbytes - offset) as maximum count not
> > > sb->s_maxbytes itself.
> > > 
> > > Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
> > 
> > Looks good to me. You can add:
> > 
> > Reviewed-by: Jan Kara <jack@suse.cz>
> 
> Yup.
> 
> What are the runtime effects of this bug?

Good question. I think ->readpage() could be called for index beyond
maximum file size supported by the filesystem leading to weird filesystem
behavior due to overflows in internal calculations.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR