[REGRESSION] coredumps truncated after "new helper: dump_align()"

[Peter Wu]

Hi Al,

Somewhere in the merge window of 3.13, coredumps appear truncated.
Instead of 319488 bytes, I get 868 bytes (tested with x86_64 only).

The latest Linus' master (v3.12-9579-g049ffa8) is still affected.
Bisection leads to:

commit 22a8cb8248ba5d340307ba72432253b1dbdb5cf7
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date:   Tue Oct 8 11:05:01 2013 -0400

    new helper: dump_align()
    
    dump_skip to given alignment...
    
    Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

:040000 040000 880920de653955485453c8cc11045bb09e2934f7 f8b348d32b59ae7a16cbc3eb2a6319f4df0210eb M      arch
:040000 040000 eaeffe2378806e95d23b3f3a9dc0fa8f078d6052 88866abde93296a05b4adda869280bc05403936f M      fs
:040000 040000 218263e01dd7473998c54a5a68ed5ae072854d24 ff531dce919862b662fef19a9a049f0de3db38ce M      include

I first noticed this bug on my laptop (v3.12-7033-g42a2d92) and
reproduced this bug in a QEMU virtual machine too. If you want, I
can also provide the git bisect script that starts QEMU and tests
the serial output. That allows a kernel to be verified in two seconds
(minus build times).

Regards,
Peter
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