• Mathieu Desnoyers's avatar
    [CPUFREQ] fix timer teardown in ondemand governor · b14893a6
    Mathieu Desnoyers authored
    * Rafael J. Wysocki (rjw@sisk.pl) wrote:
    > This message has been generated automatically as a part of a report
    > of regressions introduced between 2.6.28 and 2.6.29.
    >
    > The following bug entry is on the current list of known regressions
    > introduced between 2.6.28 and 2.6.29.  Please verify if it still should
    > be listed and let me know (either way).
    >
    >
    > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=13186
    > Subject		: cpufreq timer teardown problem
    > Submitter	: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    > Date		: 2009-04-23 14:00 (24 days old)
    > References	: http://marc.info/?l=linux-kernel&m=124049523515036&w=4
    > Handled-By	: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    > Patch		: http://patchwork.kernel.org/patch/19754/
    > 		  http://patchwork.kernel.org/patch/19753/
    >
    
    (updated changelog)
    
    cpufreq fix timer teardown in ondemand governor
    
    The problem is that dbs_timer_exit() uses cancel_delayed_work() when it should
    use cancel_delayed_work_sync(). cancel_delayed_work() does not wait for the
    workqueue handler to exit.
    
    The ondemand governor does not seem to be affected because the
    "if (!dbs_info->enable)" check at the beginning of the workqueue handler returns
    immediately without rescheduling the work. The conservative governor in
    2.6.30-rc has the same check as the ondemand governor, which makes things
    usually run smoothly. However, if the governor is quickly stopped and then
    started, this could lead to the following race :
    
    dbs_enable could be reenabled and multiple do_dbs_timer handlers would run.
    This is why a synchronized teardown is required.
    
    The following patch applies to, at least, 2.6.28.x, 2.6.29.1, 2.6.30-rc2.
    
    Depends on patch
    cpufreq: remove rwsem lock from CPUFREQ_GOV_STOP call
    Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    CC: Andrew Morton <akpm@linux-foundation.org>
    CC: gregkh@suse.de
    CC: stable@kernel.org
    CC: cpufreq@vger.kernel.org
    CC: Ingo Molnar <mingo@elte.hu>
    CC: rjw@sisk.pl
    CC: Ben Slusky <sluskyb@paranoiacs.org>
    Signed-off-by: default avatarDave Jones <davej@redhat.com>
    b14893a6
cpufreq_ondemand.c 19.3 KB