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authorMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>2009-05-17 10:29:33 -0400
committerDave Jones <davej@redhat.com>2009-05-26 12:04:50 -0400
commitb253d2b2d28ead6fed012feb54694b3d0562839a (patch)
tree39e9cb09e6e72a3029696f9b04476bc62510a77d /drivers/cpufreq
parent42a06f2166f2f6f7bf04f32b4e823eacdceafdc9 (diff)
[CPUFREQ] fix timer teardown in conservative governor
* 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/ > (re-send with updated changelog) cpufreq fix timer teardown in conservative 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. Depends on patch cpufreq: remove rwsem lock from CPUFREQ_GOV_STOP call The following patch applies to 2.6.30-rc2. Stable kernels have a similar issue which should also be fixed, but the code changed between 2.6.29 and 2.6.30, so this patch only applies to 2.6.30-rc. Signed-off-by: Mathieu 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: Dave Jones <davej@redhat.com>
Diffstat (limited to 'drivers/cpufreq')
-rw-r--r--drivers/cpufreq/cpufreq_conservative.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index 2ecd95e4ab1a..7a74d175287b 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -91,6 +91,9 @@ static unsigned int dbs_enable; /* number of CPUs using this policy */
91 * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then 91 * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then
92 * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock 92 * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock
93 * is recursive for the same process. -Venki 93 * is recursive for the same process. -Venki
94 * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, because it
95 * would deadlock with cancel_delayed_work_sync(), which is needed for proper
96 * raceless workqueue teardown.
94 */ 97 */
95static DEFINE_MUTEX(dbs_mutex); 98static DEFINE_MUTEX(dbs_mutex);
96 99
@@ -542,7 +545,7 @@ static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
542static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info) 545static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
543{ 546{
544 dbs_info->enable = 0; 547 dbs_info->enable = 0;
545 cancel_delayed_work(&dbs_info->work); 548 cancel_delayed_work_sync(&dbs_info->work);
546} 549}
547 550
548static int cpufreq_governor_dbs(struct cpufreq_policy *policy, 551static int cpufreq_governor_dbs(struct cpufreq_policy *policy,