Comment 4 for bug 830155

Bisecting finished:

9335a6a2afb9512965e3f601b887fe00479d25f1 is the first bad commit
commit 9335a6a2afb9512965e3f601b887fe00479d25f1
Author: Martin K. Petersen <email address hidden>
Date: Wed May 18 10:37:35 2011 +0200

    block: Fix discard topology stacking and reporting

    BugLink: http://bugs.launchpad.net/bugs/793702

    commit a934a00a69e940b126b9bdbf83e630ef5fe43523 upstream.

    In some cases we would end up stacking discard_zeroes_data incorrectly.
    Fix this by enabling the feature by default for stacking drivers and
    clearing it for low-level drivers. Incorporating a device that does not
    support dzd will then cause the feature to be disabled in the stacking
    driver.

    Also ensure that the maximum discard value does not overflow when
    exported in sysfs and return 0 in the alignment and dzd fields for
    devices that don't support discard.

    Reported-by: Lukas Czerner <email address hidden>
    Signed-off-by: Martin K. Petersen <email address hidden>
    Acked-by: Mike Snitzer <email address hidden>
    Signed-off-by: Jens Axboe <email address hidden>
    Signed-off-by: Greg Kroah-Hartman <email address hidden>
    Signed-off-by: Tim Gardner <email address hidden>

:040000 040000 1742d8f1c7e3f4c93e7b91f8f8bfd13c72643524 ae17fc309373c5481a6a1e94c6adceda7db2a761 M block
:040000 040000 b664df5b84192064a75346880cdc04824f6c90be 80dc258ef4dd61a2f7bc16f4c9ee1527a6b1621e M include

I'm not sure yet if it is correct. I also noticed that the bug does not appear when doing sleep before logging in, which makes me suspect it has something to do with wlan or mobile broadband. But it might also be with ecryptfs, which I use (as this commit seems to be about storage).