On 18 August 2013 19:36, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > I noticed that the current linux-next branch of linux-pm.git caused the > BUG_ON() in lock_policy_rwsem_##mode() to trigger when user space tried to > access cpufreq sysfs attributes before system suspend and after system > resume. Hmm... > I tried to debug that and it turned out that this patch caused resume > to block indefinitely on one of my test machines and after reverting it the > BUG_ON() stopped triggering, so I've just reverted it in my tree (it is not an > important change). > > I don't have the time to figure out why this change breaks things It wasn't my patch actually.. It only made it visible that's it :) The problem is: - On suspend all CPUs are removed and so governors are stopped. - On resume, handle_update() is called for the boot cpu and cpu_add_dev for all others. handle_update() doesn't start governor but only plays with CPUFREQ_GOV_LIMITS.. when we start adding other CPUs and call: cpufreq_add_policy_cpu() which fails in following call: __cpufreq_governor(policy, CPUFREQ_GOV_STOP); and so cpufreq_policy_cpu never gets initialized to policy->cpu and stays at -1, and hence the crash. So, there are few problems with core at this point: - I don't understand how does the work done in cpufreq_add_dev() gets done for boot cpu during resume ? And so how does Srivatsa's "frozen" solution really works (I haven't had time to investigate, its not that I couldn't understand it :) ).. - We need to start governor boot cpu in handle_update() and things would be solved... > and I would > appreciate it if you tested stuff like suspend/resume on an x86 laptop or > similar with your patches applied before posting them for merging. suspend/resume is broken on my ARM board and that's why didn't test it.. Testing anything on my thinkpad (with ubuntu) is a pain.. it takes more than an hour to compile/test a single image... I currently follow below steps for doing that, don't know if something much simpler/faster is available :) https://wiki.ubuntu.com/KernelTeam/GitKernelBuild Whole day I was able to boot test only 4-5 kernel builds. Its too slow :( -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
