linux-kernel - Re: [regression] fix 32-bit breakage in block device read(2) (was Re: 32-bit bug in iovec iterator changes)

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Date:	Thu, 26 Jun 2014 10:27:19 -0500
From:	Bruno Wolff III <bruno@...ff.to>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Ts'o <tytso@....edu>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Dave Chinner <david@...morbit.com>, Jens Axboe <axboe@...com>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [regression] fix 32-bit breakage in block device read(2) (was
 Re: 32-bit bug in iovec iterator changes)

On Mon, Jun 23, 2014 at 08:44:40 +0100,
  Al Viro <viro@...IV.linux.org.uk> wrote:
>
>blkdev_read_iter() wants to cap the iov_iter by the amount of
>data remaining to the end of device.  That's what iov_iter_truncate()
>is for (trim iter->count if it's above the given limit).  So far,
>so good, but the argument of iov_iter_truncate() is size_t, so on
>32bit boxen (in case of a large device) we end up with that upper
>limit truncated down to 32 bits *before* comparing it with iter->count.

This seems to fix a problem I had 
(https://bugzilla.kernel.org/show_bug.cgi?id=78711) with a partition device 
(/dev/sda3) being zero size on 3.16 kernels. However I am having some 
other issues with 3.16 on i686 and the amount of testing was the raid 
array using /dev/sda3 appeared to start (which it hadn't previously), but 
the system hung before finishing the boot process.
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